see https://github.com/festvox/flite/pull/94

--- configure.in.orig	2020-08-12 17:17:09
+++ configure.in	2023-04-20 05:11:37
@@ -239,6 +239,7 @@
 AC_SUBST(HOST_CPU)
 
 SHFLAGS=
+SHEXT="so"
 OTHERLIBS=
 
 dnl For OpenPandora and other (softfloat) ARMs with neon
@@ -273,6 +274,10 @@
 		SHFLAGS="-fPIC"
 		OTHERLIBS="-lsocket -ldl"
         ;;
+	darwin*)
+		SHFLAGS="-fPIC"
+		SHEXT="dylib"
+        ;;
 	*)
 	;;
    esac
@@ -290,6 +295,7 @@
 
 AC_SUBST(OTHERLIBS)
 AC_SUBST(SHFLAGS)
+AC_SUBST(SHEXT)
 
 AC_ARG_ENABLE( sockets,
                [  --disable-sockets     without socket support],
--- configure.orig	2020-08-12 17:17:09
+++ configure	2023-04-20 05:10:28
@@ -631,6 +631,7 @@
 STDIOTYPE
 MMAPTYPE
 SHFLAGS
+SHEXT
 OTHERLIBS
 HOST_CPU
 HOST_OS
@@ -4183,6 +4184,7 @@
 
 
 SHFLAGS=
+SHEXT=".so"
 OTHERLIBS=
 
 if grep -q Pandora /proc/cpuinfo
@@ -4220,6 +4222,10 @@
 		SHFLAGS="-fPIC"
 		OTHERLIBS="-lsocket -ldl"
         ;;
+	darwin*)
+		SHFLAGS="-fPIC"
+		SHEXT="dylib"
+        ;;
 	*)
 	;;
    esac
--- config/config.in.orig	2020-08-12 17:17:09
+++ config/config.in	2023-04-20 05:13:33
@@ -12,6 +12,7 @@
 CFLAGS   = @CFLAGS@ @ENDIANDEFS@
 CPPFLAGS = @CPPFLAGS@
 SHFLAGS  = @SHFLAGS@
+SHEXT    = @SHEXT@
 LDFLAGS  = @LDFLAGS@
 
 AR       = @AR@
--- main/Makefile.orig	2020-08-12 17:17:09
+++ main/Makefile	2023-04-20 06:42:59
@@ -65,13 +65,18 @@
 # We need to set these vars, even if we're not going to build them
 # so make clean can remove them
 SHAREDARLIBS= $(flite_LIBS:%=$(LIBDIR)/lib%.shared.a)
-SHAREDLIBS = $(SHAREDARLIBS:%.shared.a=%.so)
-SHAREDMODS = $(flite_MODS:%=$(LIBDIR)/lib%.so)
-SHAREDusenMODS = $(LIBDIR)/libflite_cmu_time_awb.so $(LIBDIR)/libflite_cmu_us_awb.so $(LIBDIR)/libflite_cmu_us_kal16.so $(LIBDIR)/libflite_cmu_us_kal.so $(LIBDIR)/libflite_cmu_us_rms.so $(LIBDIR)/libflite_cmu_us_slt.so $(LIBDIR)/libflite_cmu_indic_lang.so
-SHAREDcmulexMODS = $(LIBDIR)/libflite_cmu_time_awb.so $(LIBDIR)/libflite_cmu_us_awb.so $(LIBDIR)/libflite_cmu_us_kal16.so $(LIBDIR)/libflite_cmu_us_kal.so $(LIBDIR)/libflite_cmu_us_rms.so $(LIBDIR)/libflite_cmu_us_slt.so  $(LIBDIR)/libflite_cmu_indic_lex.so
-SHAREDindicMODS = $(LIBDIR)/libflite_cmu_indic_lex.so
+SHAREDLIBS = $(SHAREDARLIBS:%.shared.a=%.$(SHEXT))
+SHAREDMODS = $(flite_MODS:%=$(LIBDIR)/lib%.$(SHEXT))
+SHAREDusenMODS = $(LIBDIR)/libflite_cmu_time_awb.$(SHEXT) $(LIBDIR)/libflite_cmu_us_awb.$(SHEXT) $(LIBDIR)/libflite_cmu_us_kal16.$(SHEXT) $(LIBDIR)/libflite_cmu_us_kal.$(SHEXT) $(LIBDIR)/libflite_cmu_us_rms.$(SHEXT) $(LIBDIR)/libflite_cmu_us_slt.$(SHEXT) $(LIBDIR)/libflite_cmu_indic_lang.$(SHEXT)
+SHAREDcmulexMODS = $(LIBDIR)/libflite_cmu_time_awb.$(SHEXT) $(LIBDIR)/libflite_cmu_us_awb.$(SHEXT) $(LIBDIR)/libflite_cmu_us_kal16.$(SHEXT) $(LIBDIR)/libflite_cmu_us_kal.$(SHEXT) $(LIBDIR)/libflite_cmu_us_rms.$(SHEXT) $(LIBDIR)/libflite_cmu_us_slt.$(SHEXT)  $(LIBDIR)/libflite_cmu_indic_lex.$(SHEXT)
+SHAREDindicMODS = $(LIBDIR)/libflite_cmu_indic_lex.$(SHEXT)
+ifneq ($(SHEXT),dylib)
 VERSIONSHAREDLIBS = $(SHAREDLIBS:%=%.${PROJECT_VERSION}) \
                     $(SHAREDLIBS:%=%.${PROJECT_SHLIB_VERSION})
+else
+VERSIONSHAREDLIBS = $(SHAREDLIBS:%$(SHEXT)=%${PROJECT_VERSION}.$(SHEXT)) \
+                    $(SHAREDLIBS:%$(SHEXT)=%${PROJECT_SHLIB_VERSION}.$(SHEXT))
+endif
 
 flite_time_LIBS = flite_cmu_time_awb flite_usenglish flite_cmulex
 flite_time_LIBS_flags = -L$(LIBDIR) $(flite_time_LIBS:%=-l%)
@@ -84,13 +89,13 @@
               flite_voice_list.c
 
 ifdef SHFLAGS
-$(SHAREDMODS): $(LIBDIR)/libflite.so
+$(SHAREDMODS): $(LIBDIR)/libflite.$(SHEXT)
 $(SHAREDMODS): LDFLAGS+=-L../$(LIBDIR) -lflite
-$(SHAREDusenMODS): $(LIBDIR)/libflite_usenglish.so
+$(SHAREDusenMODS): $(LIBDIR)/libflite_usenglish.$(SHEXT)
 $(SHAREDusenMODS): LDFLAGS+=-L../$(LIBDIR) -lflite_usenglish
-$(SHAREDcmulexMODS): $(LIBDIR)/libflite_cmulex.so
+$(SHAREDcmulexMODS): $(LIBDIR)/libflite_cmulex.$(SHEXT)
 $(SHAREDcmulexMODS): LDFLAGS+=-L../$(LIBDIR) -lflite_cmulex
-$(SHAREDindicMODS): $(LIBDIR)/libflite_cmu_indic_lang.so
+$(SHAREDindicMODS): $(LIBDIR)/libflite_cmu_indic_lang.$(SHEXT)
 $(SHAREDindicMODS): LDFLAGS+=-L../$(LIBDIR) -lflite_cmu_indic_lang
 shared_libs: $(SHAREDLIBS)
 else
--- config/common_make_rules.orig	2020-08-12 17:17:09
+++ config/common_make_rules	2023-04-19 13:47:12
@@ -128,6 +128,17 @@
 	@ (cd $(LIBDIR) && ln -s `basename $@.${PROJECT_SHLIB_VERSION}` `basename $@` )
 	@ rm -rf shared_os
 
+# Used in the lib/ directory and in building new voices
+$(LIBDIR)/%.dylib: $(LIBDIR)/%.shared.a
+	@ echo making $@
+	@ rm -rf shared_os && mkdir shared_os
+	@ rm -f $@ $@.${PROJECT_VERSION} $@.${PROJECT_SHLIB_VERSION}
+	@ (cd shared_os && ar x ../$<)
+	@ (cd shared_os && $(CC) -dynamiclib -install_name ${INSTALLLIBDIR}/`basename $@ ${SHEXT}`${PROJECT_SHLIB_VERSION}.${SHEXT} -current_version ${PROJECT_VERSION} -compatibility_version ${PROJECT_SHLIB_VERSION} -o ../${@:${SHEXT}=${PROJECT_VERSION}.${SHEXT}} *.os $(LDFLAGS) $(addprefix ../,$(filter-out $<,${^:${SHEXT}=${PROJECT_VERSION}.${SHEXT}})))
+	@ (cd $(LIBDIR) && ln -s `basename $@ ${SHEXT}`${PROJECT_VERSION}.${SHEXT} `basename $@ ${SHEXT}`${PROJECT_SHLIB_VERSION}.${SHEXT} )
+	@ (cd $(LIBDIR) && ln -s `basename $@ ${SHEXT}`${PROJECT_SHLIB_VERSION}.${SHEXT} `basename $@` )
+	@ rm -rf shared_os
+
 $(OBJDIR)/.make_build_dirs:
 	@ echo making in $(DIRNAME) ...
 ifdef BUILD_DIRS