[sparc64/base-gcc] Fix build of net/wget on sparc64

I've been carrying this patch for a while, I had forgotten about it.

net/wget has joined the march of C99-using ports. I've done the usual
things to make base-gcc do the right thing.

This fixes the build on sparc64.

ok?

(cc maintainer)

--Kurt

Index: Makefile
===================================================================
RCS file: /cvs/ports/net/wget/Makefile,v
retrieving revision 1.87
diff -u -p -r1.87 Makefile
--- Makefile 27 Jun 2021 23:49:58 -0000 1.87
+++ Makefile 29 Jun 2021 21:17:39 -0000
@@ -46,4 +46,10 @@ MODGNU_CONFIG_GUESS_DIRS = ${WRKSRC}/bui
pre-build:
@${SUBST_CMD} ${WRKSRC}/doc/wget.texi ${WRKSRC}/doc/sample.wgetrc

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