[ports-gcc] unbreak graphics/spirv-tools and graphics/glslang

Hi,

I'm grouping these two as they've the same issue; this is C++11 code
and they can't be built with base-gcc.

There is no REVISION bump needed - they've never been built on
base-gcc archs.

OK?

Charlène.

> http://build-failures.rhaalovely.net//powerpc/2019-07-14/graphics/spirv-tools.log

Index: Makefile
===================================================================
RCS file: /cvs/ports/graphics/spirv-tools/Makefile,v
retrieving revision 1.2
diff -u -p -u -p -r1.2 Makefile
--- Makefile 22 Jun 2019 16:51:06 -0000 1.2
+++ Makefile 26 Jul 2019 12:19:50 -0000
@@ -18,6 +18,9 @@ PERMIT_PACKAGE = Yes

WANTLIB += ${COMPILER_LIBCXX} c m

+# C++11
+COMPILER = base-clang ports-gcc
+
MODULES = devel/cmake
BUILD_DEPENDS = graphics/spirv-headers

> http://build-failures.rhaalovely.net//powerpc/2019-07-14/graphics/glslang.log

Index: Makefile
===================================================================
RCS file: /cvs/ports/graphics/glslang/Makefile,v
retrieving revision 1.2
diff -u -p -u -p -r1.2 Makefile
--- Makefile 22 Jun 2019 16:48:25 -0000 1.2
+++ Makefile 26 Jul 2019 12:24:45 -0000
@@ -16,6 +16,9 @@ PERMIT_PACKAGE = Yes

WANTLIB += ${COMPILER_LIBCXX} c m

+# C++11
+COMPILER = base-clang ports-gcc
+
MODULES = devel/cmake
TEST_DEPENDS = graphics/spirv-tools \
shells/bash