[sparc64/base-gcc] Fix build of graphics/mojoshader

[Kurt Mosiejczuk]

mojoshader uses C99 constructs so base-gcc needs to be informed of that.
This diff fixes the build on sparc64

ok?

(cc maintainer)

--Kurt

Index: Makefile
===================================================================
RCS file: /cvs/ports/graphics/mojoshader/Makefile,v
retrieving revision 1.8
diff -u -p -r1.8 Makefile
--- Makefile    17 Dec 2020 07:45:16 -0000      1.8
+++ Makefile    9 Jan 2021 17:21:56 -0000
@@ -40,6 +40,11 @@ WRKDIST =    ${WRKDIR}/mojoshader-${HG_COMM
 
 SUBST_VARS +=  HG_CHANGESET HG_COMMIT
 
+.include <bsd.port.arch.mk>
+.if !${PROPERTIES:Mclang}
+CFLAGS +=      -std=gnu99
+.endif
+
 do-gen:
        ${SUBST_CMD} ${WRKSRC}/CMakeLists.txt