gtk4: fix older systems

gtk4 can't Werror on missing declarations, because GLIB defines
macros to nothing based on compiler support, etc.

legacysupport is needed for missing defines, at least

gnome/gtk4/Portfile

@@ -3,8 +3,10 @@
 PortSystem          1.0
 PortGroup           meson 1.0
 PortGroup           active_variants 1.1
-#PortGroup           legacysupport 1.1
+PortGroup           legacysupport 1.1
 
+# O_CLOEXEC
+legacysupport.newest_darwin_requires_legacy 10
 
 name                gtk4
 #conflicts           gtk4-devel
@@ -67,6 +69,8 @@ patchfiles-append   patch-docs-rst2man.diff
 
 patchfiles-append   patch-testsuite-python.diff
 
+patchfiles-append   patch-meson-dont-werror-on-missing-declarations.diff
+
 post-patch {
     reinplace "s|@@PYTHON_VERSION@@|${python_branch}|" \
         ${worksrcpath}/docs/reference/gtk/meson.build  \

gnome/gtk4/files/patch-meson-dont-werror-on-missing-declarations.diff

@@ -0,0 +1,14 @@
+GLIB uses the technique of defining the macro to nothing
+if it can't be used on a given compiler. But having this
+defined to nothing generates a Werror, so that can't work.
+
+--- meson.build.orig	2022-11-02 00:37:51.000000000 -0700
++++ meson.build	2022-11-02 00:38:13.000000000 -0700
+@@ -306,7 +306,6 @@
+     'int-to-pointer-cast',
+     'main',
+     'missing-braces',
+-    'missing-declarations',
+     'missing-prototypes',
+     'nonnull',
+     'pointer-to-int-cast',