[base-gcc/sparc64] Fix build of telephony/linphone/*

Most parts of linphone require a compiler that does C++11, which rules out
base-gcc.

This patch patches the Makefile.inc to cover all those ports and fixes the
build on sparc64.

ok?

(cc maintainer)

--Kurt

Index: Makefile.inc
===================================================================
RCS file: /cvs/ports/telephony/linphone/Makefile.inc,v
retrieving revision 1.2
diff -u -p -r1.2 Makefile.inc
--- Makefile.inc 10 Jul 2021 16:55:23 -0000 1.2
+++ Makefile.inc 9 Aug 2021 15:19:17 -0000
@@ -7,5 +7,7 @@ MASTER_SITES = https://gitlab.linphone.o
DISTNAME ?= ${MODULE}-${V}
MAINTAINER = Landry Breuil <landry@openbsd.org>

+COMPILER = base-clang ports-gcc
+
# GPLv3
PERMIT_PACKAGE = Yes