Do not set -arch flags. MacPorts will do that.
--- meson.build.orig	2023-07-28 08:38:44.000000000 -0500
+++ meson.build	2023-08-01 05:44:45.000000000 -0500
@@ -451,17 +451,6 @@
     '-exported_symbols_list', meson.current_source_dir() / 'vamp/vamp-plugin.list'
   ]
 
-  if architecture == 'aarch64'
-    arch_flags += [
-      '-arch', 'arm64',
-    ]
-  elif architecture == 'x86_64'
-    arch_flags += [
-      '-arch', 'x86_64',
-    ]
-  else # begin architecture != 'aarch64' or 'x86_64'
-    error('Build for architecture ' + architecture + ' is not supported on this platform')
-  endif # end architecture
 
   have_version_min = false
   foreach arg: get_option('cpp_args')