[base-gcc/sparc64] Fix build of x11/roxterm

[Kurt Mosiejczuk]

x11/roxterm needs C99 for a for loop.

This diff fixes the build on sparc64.

ok?

--Kurt

Index: Makefile
===================================================================
RCS file: /cvs/ports/x11/roxterm/Makefile,v
retrieving revision 1.50
diff -u -p -r1.50 Makefile
--- Makefile    11 Feb 2021 10:20:04 -0000      1.50
+++ Makefile    16 May 2021 03:21:38 -0000
@@ -25,6 +25,11 @@ LIB_DEPENDS=         devel/vte3 \
 RUN_DEPENDS=           devel/desktop-file-utils \
                        x11/gtk+3,-guic
 
+.include <bsd.port.arch.mk>
+.if !${PROPERTIES:Mclang}
+CFLAGS +=      -std=gnu99
+.endif
+
 NO_TEST=               Yes
 
 .include <bsd.port.mk>