[librsvg/wip/chergert/fix-macos-link] build: use -framework Foundation on macOS

[Christian Hergert <chergert src gnome org>]

commit 474b4c21d1f24261627a93a636e9a36190bdca88
Author: Christian Hergert <chergert redhat com>
Date:   Fri Nov 27 20:58:33 2020 -0800

    build: use -framework Foundation on macOS
    
    This fixes an issue where link symbols are not available for basic Obj-C
    message passing and other release/retain operations.
    
    Fixes #545

 Makefile.am  |  4 ++++
 configure.ac | 16 ++++++++++++++++
 2 files changed, 20 insertions(+)
---
diff --git a/Makefile.am b/Makefile.am
index 9013a95e..d9204fd5 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -204,6 +204,10 @@ librsvg_@RSVG_API_MAJOR_VERSION@_la_LDFLAGS = \
        -export-symbols-regex "^rsvg_.*" \
        $(AM_LDFLAGS)
 
+if OS_DARWIN
+librsvg_@RSVG_API_MAJOR_VERSION@_la_LDFLAGS += -framework Foundation
+endif
+
 librsvg_@RSVG_API_MAJOR_VERSION@_la_LIBADD = \
        librsvg_c_api.la        \
        $(LIBRSVG_LIBS)         \
diff --git a/configure.ac b/configure.ac
index 60394eec..428b7e73 100644
--- a/configure.ac
+++ b/configure.ac
@@ -157,6 +157,22 @@ AM_CONDITIONAL(OS_WIN32, test "$native_win32" = "yes")
 
 dnl ===========================================================================
 
+#AC_CANONICAL_HOST
+
+AC_MSG_CHECKING([for darwin])
+case "$host" in
+  darwin*)
+    native_darwin=yes
+    ;;
+  *)
+    native_darwin=no
+    ;;
+esac
+AC_MSG_RESULT([$native_darwin])
+AM_CONDITIONAL(OS_DARWIN, test "$native_darwin" = "yes")
+
+dnl ===========================================================================
+
 GLIB_MKENUMS=`$PKG_CONFIG --variable=glib_mkenums glib-2.0`
 AC_SUBST(GLIB_MKENUMS)