app: add some CPPFLAGS in core/Makefile.am to fix the build on OSX

app/core/Makefile.am

@@ -1,7 +1,13 @@
 ## Process this file with automake to produce Makefile.in
 
+if PLATFORM_OSX
+xobjective_c = "-xobjective-c"
+endif
+
 AM_CPPFLAGS = \
+	-DGIMPDIR=\""$(gimpdir)"\"			\
 	-DGIMP_APP_VERSION=\"$(GIMP_APP_VERSION)\"	\
+	-DGIMP_USER_VERSION=\"$(GIMP_USER_VERSION)\"	\
 	-DG_LOG_DOMAIN=\"Gimp-Core\"			\
 	-I$(top_builddir)				\
 	-I$(top_srcdir)					\
@@ -11,7 +17,8 @@ AM_CPPFLAGS = \
 	$(GEGL_CFLAGS)					\
 	$(GDK_PIXBUF_CFLAGS)				\
 	$(GEXIV2_CFLAGS)				\
-	-I$(includedir)
+	-I$(includedir)					\
+	$(xobjective_c)
 
 noinst_LIBRARIES = libappcore.a