[sparc64/base-hcc] Fix build of devel/glade

Another C99 port. Needs the following to compile on sparc64 and other
base-gcc arches.

ok?

--Kurt

Index: Makefile
===================================================================
RCS file: /cvs/ports/devel/glade/Makefile,v
retrieving revision 1.88
diff -u -p -r1.88 Makefile
--- Makefile 14 May 2020 15:13:34 -0000 1.88
+++ Makefile 27 Jun 2020 00:52:33 -0000
@@ -45,6 +45,11 @@ MODGNOME_TOOLS += gobject-introspection
CONFIGURE_STYLE= gnu
CONFIGURE_ARGS += --disable-webkit2gtk

+.include <bsd.port.arch.mk>
+.if !${PROPERTIES:Mclang}
+CFLAGS += -std=gnu99
+.endif
+
DEBUG_PACKAGES = ${BUILD_PACKAGES}

post-install: