Recognize macOS 11 and later, remove inaccurate comment, and simplify.
https://debbugs.gnu.org/cgi/bugreport.cgi?bug=44605
--- configure.orig	2005-10-03 04:28:58.000000000 -0500
+++ configure	2021-07-26 15:28:42.000000000 -0500
@@ -7403,18 +7403,14 @@
          allow_undefined_flag='${wl}-undefined ${wl}suppress'
          ;;
        *) # Darwin 1.3 on
-         if test -z ${MACOSX_DEPLOYMENT_TARGET} ; then
-           allow_undefined_flag='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
-         else
-           case ${MACOSX_DEPLOYMENT_TARGET} in
-             10.[012])
+           case $MACOSX_DEPLOYMENT_TARGET,$host in
+             10.[012],*|,*powerpc*-darwin[5-8]*)
                allow_undefined_flag='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
                ;;
-             10.*)
+             *)
                allow_undefined_flag='${wl}-undefined ${wl}dynamic_lookup'
                ;;
            esac
-         fi
          ;;
       esac
       archive_cmds_need_lc=no
@@ -10390,18 +10386,14 @@
          allow_undefined_flag_CXX='${wl}-undefined ${wl}suppress'
          ;;
        *) # Darwin 1.3 on
-         if test -z ${MACOSX_DEPLOYMENT_TARGET} ; then
-           allow_undefined_flag_CXX='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
-         else
-           case ${MACOSX_DEPLOYMENT_TARGET} in
-             10.[012])
+           case $MACOSX_DEPLOYMENT_TARGET,$host in
+             10.[012],*|,*powerpc*-darwin[5-8]*)
                allow_undefined_flag_CXX='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
                ;;
-             10.*)
+             *)
                allow_undefined_flag_CXX='${wl}-undefined ${wl}dynamic_lookup'
                ;;
            esac
-         fi
          ;;
         esac
       archive_cmds_need_lc_CXX=no
@@ -14472,18 +14464,14 @@
          allow_undefined_flag_F77='${wl}-undefined ${wl}suppress'
          ;;
        *) # Darwin 1.3 on
-         if test -z ${MACOSX_DEPLOYMENT_TARGET} ; then
-           allow_undefined_flag_F77='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
-         else
-           case ${MACOSX_DEPLOYMENT_TARGET} in
-             10.[012])
+           case $MACOSX_DEPLOYMENT_TARGET,$host in
+             10.[012],*|,*powerpc*-darwin[5-8]*)
                allow_undefined_flag_F77='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
                ;;
-             10.*)
+             *)
                allow_undefined_flag_F77='${wl}-undefined ${wl}dynamic_lookup'
                ;;
            esac
-         fi
          ;;
       esac
       archive_cmds_need_lc_F77=no
@@ -16950,18 +16938,14 @@
          allow_undefined_flag_GCJ='${wl}-undefined ${wl}suppress'
          ;;
        *) # Darwin 1.3 on
-         if test -z ${MACOSX_DEPLOYMENT_TARGET} ; then
-           allow_undefined_flag_GCJ='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
-         else
-           case ${MACOSX_DEPLOYMENT_TARGET} in
-             10.[012])
+           case $MACOSX_DEPLOYMENT_TARGET,$host in
+             10.[012],*|,*powerpc*-darwin[5-8]*)
                allow_undefined_flag_GCJ='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
                ;;
-             10.*)
+             *)
                allow_undefined_flag_GCJ='${wl}-undefined ${wl}dynamic_lookup'
                ;;
            esac
-         fi
          ;;
       esac
       archive_cmds_need_lc_GCJ=no
--- lib_cfg/configure.orig	2005-10-03 04:29:04.000000000 -0500
+++ lib_cfg/configure	2021-07-26 15:28:42.000000000 -0500
@@ -7338,18 +7338,14 @@
          allow_undefined_flag='${wl}-undefined ${wl}suppress'
          ;;
        *) # Darwin 1.3 on
-         if test -z ${MACOSX_DEPLOYMENT_TARGET} ; then
-           allow_undefined_flag='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
-         else
-           case ${MACOSX_DEPLOYMENT_TARGET} in
-             10.[012])
+           case $MACOSX_DEPLOYMENT_TARGET,$host in
+             10.[012],*|,*powerpc*-darwin[5-8]*)
                allow_undefined_flag='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
                ;;
-             10.*)
+             *)
                allow_undefined_flag='${wl}-undefined ${wl}dynamic_lookup'
                ;;
            esac
-         fi
          ;;
       esac
       archive_cmds_need_lc=no
@@ -10325,18 +10321,14 @@
          allow_undefined_flag_CXX='${wl}-undefined ${wl}suppress'
          ;;
        *) # Darwin 1.3 on
-         if test -z ${MACOSX_DEPLOYMENT_TARGET} ; then
-           allow_undefined_flag_CXX='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
-         else
-           case ${MACOSX_DEPLOYMENT_TARGET} in
-             10.[012])
+           case $MACOSX_DEPLOYMENT_TARGET,$host in
+             10.[012],*|,*powerpc*-darwin[5-8]*)
                allow_undefined_flag_CXX='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
                ;;
-             10.*)
+             *)
                allow_undefined_flag_CXX='${wl}-undefined ${wl}dynamic_lookup'
                ;;
            esac
-         fi
          ;;
         esac
       archive_cmds_need_lc_CXX=no
@@ -14407,18 +14399,14 @@
          allow_undefined_flag_F77='${wl}-undefined ${wl}suppress'
          ;;
        *) # Darwin 1.3 on
-         if test -z ${MACOSX_DEPLOYMENT_TARGET} ; then
-           allow_undefined_flag_F77='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
-         else
-           case ${MACOSX_DEPLOYMENT_TARGET} in
-             10.[012])
+           case $MACOSX_DEPLOYMENT_TARGET,$host in
+             10.[012],*|,*powerpc*-darwin[5-8]*)
                allow_undefined_flag_F77='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
                ;;
-             10.*)
+             *)
                allow_undefined_flag_F77='${wl}-undefined ${wl}dynamic_lookup'
                ;;
            esac
-         fi
          ;;
       esac
       archive_cmds_need_lc_F77=no
@@ -16885,18 +16873,14 @@
          allow_undefined_flag_GCJ='${wl}-undefined ${wl}suppress'
          ;;
        *) # Darwin 1.3 on
-         if test -z ${MACOSX_DEPLOYMENT_TARGET} ; then
-           allow_undefined_flag_GCJ='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
-         else
-           case ${MACOSX_DEPLOYMENT_TARGET} in
-             10.[012])
+           case $MACOSX_DEPLOYMENT_TARGET,$host in
+             10.[012],*|,*powerpc*-darwin[5-8]*)
                allow_undefined_flag_GCJ='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
                ;;
-             10.*)
+             *)
                allow_undefined_flag_GCJ='${wl}-undefined ${wl}dynamic_lookup'
                ;;
            esac
-         fi
          ;;
       esac
       archive_cmds_need_lc_GCJ=no
--- lib_l2/configure.orig	2005-10-03 04:29:01.000000000 -0500
+++ lib_l2/configure	2021-07-26 15:28:42.000000000 -0500
@@ -6985,18 +6985,14 @@
          allow_undefined_flag='${wl}-undefined ${wl}suppress'
          ;;
        *) # Darwin 1.3 on
-         if test -z ${MACOSX_DEPLOYMENT_TARGET} ; then
-           allow_undefined_flag='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
-         else
-           case ${MACOSX_DEPLOYMENT_TARGET} in
-             10.[012])
+           case $MACOSX_DEPLOYMENT_TARGET,$host in
+             10.[012],*|,*powerpc*-darwin[5-8]*)
                allow_undefined_flag='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
                ;;
-             10.*)
+             *)
                allow_undefined_flag='${wl}-undefined ${wl}dynamic_lookup'
                ;;
            esac
-         fi
          ;;
       esac
       archive_cmds_need_lc=no
@@ -9972,18 +9968,14 @@
          allow_undefined_flag_CXX='${wl}-undefined ${wl}suppress'
          ;;
        *) # Darwin 1.3 on
-         if test -z ${MACOSX_DEPLOYMENT_TARGET} ; then
-           allow_undefined_flag_CXX='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
-         else
-           case ${MACOSX_DEPLOYMENT_TARGET} in
-             10.[012])
+           case $MACOSX_DEPLOYMENT_TARGET,$host in
+             10.[012],*|,*powerpc*-darwin[5-8]*)
                allow_undefined_flag_CXX='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
                ;;
-             10.*)
+             *)
                allow_undefined_flag_CXX='${wl}-undefined ${wl}dynamic_lookup'
                ;;
            esac
-         fi
          ;;
         esac
       archive_cmds_need_lc_CXX=no
@@ -14054,18 +14046,14 @@
          allow_undefined_flag_F77='${wl}-undefined ${wl}suppress'
          ;;
        *) # Darwin 1.3 on
-         if test -z ${MACOSX_DEPLOYMENT_TARGET} ; then
-           allow_undefined_flag_F77='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
-         else
-           case ${MACOSX_DEPLOYMENT_TARGET} in
-             10.[012])
+           case $MACOSX_DEPLOYMENT_TARGET,$host in
+             10.[012],*|,*powerpc*-darwin[5-8]*)
                allow_undefined_flag_F77='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
                ;;
-             10.*)
+             *)
                allow_undefined_flag_F77='${wl}-undefined ${wl}dynamic_lookup'
                ;;
            esac
-         fi
          ;;
       esac
       archive_cmds_need_lc_F77=no
@@ -16532,18 +16520,14 @@
          allow_undefined_flag_GCJ='${wl}-undefined ${wl}suppress'
          ;;
        *) # Darwin 1.3 on
-         if test -z ${MACOSX_DEPLOYMENT_TARGET} ; then
-           allow_undefined_flag_GCJ='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
-         else
-           case ${MACOSX_DEPLOYMENT_TARGET} in
-             10.[012])
+           case $MACOSX_DEPLOYMENT_TARGET,$host in
+             10.[012],*|,*powerpc*-darwin[5-8]*)
                allow_undefined_flag_GCJ='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
                ;;
-             10.*)
+             *)
                allow_undefined_flag_GCJ='${wl}-undefined ${wl}dynamic_lookup'
                ;;
            esac
-         fi
          ;;
       esac
       archive_cmds_need_lc_GCJ=no
--- lib_pcre/configure.orig	2005-10-03 04:29:07.000000000 -0500
+++ lib_pcre/configure	2021-07-26 15:28:42.000000000 -0500
@@ -7145,18 +7145,14 @@
          allow_undefined_flag='${wl}-undefined ${wl}suppress'
          ;;
        *) # Darwin 1.3 on
-         if test -z ${MACOSX_DEPLOYMENT_TARGET} ; then
-           allow_undefined_flag='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
-         else
-           case ${MACOSX_DEPLOYMENT_TARGET} in
-             10.[012])
+           case $MACOSX_DEPLOYMENT_TARGET,$host in
+             10.[012],*|,*powerpc*-darwin[5-8]*)
                allow_undefined_flag='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
                ;;
-             10.*)
+             *)
                allow_undefined_flag='${wl}-undefined ${wl}dynamic_lookup'
                ;;
            esac
-         fi
          ;;
       esac
       archive_cmds_need_lc=no
@@ -10132,18 +10128,14 @@
          allow_undefined_flag_CXX='${wl}-undefined ${wl}suppress'
          ;;
        *) # Darwin 1.3 on
-         if test -z ${MACOSX_DEPLOYMENT_TARGET} ; then
-           allow_undefined_flag_CXX='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
-         else
-           case ${MACOSX_DEPLOYMENT_TARGET} in
-             10.[012])
+           case $MACOSX_DEPLOYMENT_TARGET,$host in
+             10.[012],*|,*powerpc*-darwin[5-8]*)
                allow_undefined_flag_CXX='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
                ;;
-             10.*)
+             *)
                allow_undefined_flag_CXX='${wl}-undefined ${wl}dynamic_lookup'
                ;;
            esac
-         fi
          ;;
         esac
       archive_cmds_need_lc_CXX=no
@@ -14214,18 +14206,14 @@
          allow_undefined_flag_F77='${wl}-undefined ${wl}suppress'
          ;;
        *) # Darwin 1.3 on
-         if test -z ${MACOSX_DEPLOYMENT_TARGET} ; then
-           allow_undefined_flag_F77='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
-         else
-           case ${MACOSX_DEPLOYMENT_TARGET} in
-             10.[012])
+           case $MACOSX_DEPLOYMENT_TARGET,$host in
+             10.[012],*|,*powerpc*-darwin[5-8]*)
                allow_undefined_flag_F77='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
                ;;
-             10.*)
+             *)
                allow_undefined_flag_F77='${wl}-undefined ${wl}dynamic_lookup'
                ;;
            esac
-         fi
          ;;
       esac
       archive_cmds_need_lc_F77=no
@@ -16692,18 +16680,14 @@
          allow_undefined_flag_GCJ='${wl}-undefined ${wl}suppress'
          ;;
        *) # Darwin 1.3 on
-         if test -z ${MACOSX_DEPLOYMENT_TARGET} ; then
-           allow_undefined_flag_GCJ='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
-         else
-           case ${MACOSX_DEPLOYMENT_TARGET} in
-             10.[012])
+           case $MACOSX_DEPLOYMENT_TARGET,$host in
+             10.[012],*|,*powerpc*-darwin[5-8]*)
                allow_undefined_flag_GCJ='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
                ;;
-             10.*)
+             *)
                allow_undefined_flag_GCJ='${wl}-undefined ${wl}dynamic_lookup'
                ;;
            esac
-         fi
          ;;
       esac
       archive_cmds_need_lc_GCJ=no