Makefiles: don't use -xobjective-c when compiling C++ files on Mac

On Mac, pass -xobjective-c to the compiler through AM_CFLAGS, not
AM_CPPFLAGS, so that it's only used for C sources, and not C++
sources.  In the latter case, it clashes with the -std=... flag,
spewing an error.  Thanks, Partha :)

app-tools/Makefile.am

@@ -67,5 +67,7 @@ AM_CPPFLAGS = \
 	-DGIMP_PLUGIN_VERSION=\""$(GIMP_PLUGIN_VERSION)"\"	\
 	-I$(top_srcdir)						\
 	$(GTK_CFLAGS)						\
-	-I$(includedir)						\
+	-I$(includedir)
+
+AM_CFLAGS = \
 	$(xobjective_c)

app/core/Makefile.am

@@ -18,7 +18,9 @@ AM_CPPFLAGS = \
 	$(GDK_PIXBUF_CFLAGS)				\
 	$(LIBMYPAINT_CFLAGS)				\
 	$(GEXIV2_CFLAGS)				\
-	-I$(includedir)					\
+	-I$(includedir)
+
+AM_CFLAGS = \
 	$(xobjective_c)
 
 noinst_LIBRARIES = libappcore.a

app/display/Makefile.am

@@ -12,7 +12,9 @@ AM_CPPFLAGS = \
 	-I$(top_srcdir)/app		\
 	$(GEGL_CFLAGS)			\
 	$(GTK_CFLAGS)			\
-	-I$(includedir)			\
+	-I$(includedir)
+
+AM_CFLAGS = \
 	$(xobjective_c)
 
 noinst_LIBRARIES = libappdisplay.a

app/gui/Makefile.am

@@ -11,7 +11,6 @@ AM_CPPFLAGS = \
 	-I$(top_srcdir)				\
 	-I$(top_builddir)/app			\
 	-I$(top_srcdir)/app			\
-	$(xobjective_c)				\
 	$(GIO_UNIX_CFLAGS)			\
 	$(GEGL_CFLAGS)				\
 	$(GTK_CFLAGS)				\
@@ -19,6 +18,9 @@ AM_CPPFLAGS = \
 	$(DBUS_GLIB_CFLAGS)			\
 	-I$(includedir)
 
+AM_CFLAGS = \
+	$(xobjective_c)
+
 noinst_LIBRARIES = libappgui.a
 
 libappgui_a_sources = \

app/widgets/Makefile.am

@@ -14,7 +14,9 @@ AM_CPPFLAGS = \
 	-I$(top_srcdir)/app					\
 	$(GEGL_CFLAGS)						\
 	$(GTK_CFLAGS)						\
-	-I$(includedir)						\
+	-I$(includedir)
+
+AM_CFLAGS = \
 	$(xobjective_c)
 
 noinst_LIBRARIES = libappwidgets.a

libgimp/Makefile.am

@@ -75,7 +75,9 @@ AM_CPPFLAGS = \
 	$(GTK_CFLAGS)			\
 	$(GEGL_CFLAGS)			\
 	$(GEXIV2_CFLAGS)		\
-	-I$(includedir)			\
+	-I$(includedir)
+
+AM_CFLAGS = \
 	$(xobjective_c)
 
 lib_LTLIBRARIES = libgimp-@GIMP_API_VERSION@.la libgimpui-@GIMP_API_VERSION@.la

libgimpbase/Makefile.am

@@ -64,7 +64,9 @@ AM_CPPFLAGS = \
 	$(GIO_CFLAGS)						\
 	$(GEXIV2_CFLAGS)					\
 	$(BINRELOC_CFLAGS)					\
-	-I$(includedir)						\
+	-I$(includedir)
+
+AM_CFLAGS = \
 	$(xobjective_c)
 
 AM_CCASFLAGS = \

libgimpthumb/Makefile.am

@@ -50,7 +50,9 @@ AM_CPPFLAGS = \
 	-I$(top_srcdir)			\
 	$(GDK_PIXBUF_CFLAGS)		\
 	$(GIO_CFLAGS)			\
-	-I$(includedir)			\
+	-I$(includedir)
+
+AM_CFLAGS = \
 	$(xobjective_c)
 
 EXTRA_DIST = \

libgimpwidgets/Makefile.am

@@ -58,7 +58,9 @@ AM_CPPFLAGS = \
 	$(GEGL_CFLAGS)				\
 	$(GTK_CFLAGS)				\
 	$(LCMS_CFLAGS)				\
-	-I$(includedir)				\
+	-I$(includedir)
+
+AM_CFLAGS = \
 	$(xobjective_c)
 
 lib_LTLIBRARIES = libgimpwidgets-@GIMP_API_VERSION@.la

plug-ins/script-fu/Makefile.am

@@ -31,14 +31,14 @@ endif
 AM_CFLAGS = \
 	-DSTANDALONE=0		\
 	-DUSE_INTERFACE=1	\
-	-DUSE_STRLWR=0
+	-DUSE_STRLWR=0		\
+	$(xobjective_c)
 
 AM_CPPFLAGS = \
 	-I$(top_srcdir)	\
 	$(GTK_CFLAGS)	\
 	$(GEGL_CFLAGS)	\
-	-I$(includedir)	\
+	-I$(includedir)
-	$(xobjective_c)
 
 AM_LDFLAGS = \
 	$(mwindows)	\

tools/Makefile.am

@@ -87,7 +87,9 @@ AM_CPPFLAGS = \
 	-DGIMP_PLUGIN_VERSION=\""$(GIMP_PLUGIN_VERSION)"\"	\
 	-I$(top_srcdir)						\
 	$(GTK_CFLAGS)						\
-	-I$(includedir)						\
+	-I$(includedir)
+
+AM_CFLAGS = \
 	$(xobjective_c)
 
 EXTRA_DIST = \