Remove '-Wno-unused-but-set-variable' on GCC-based systems to fix build:

cc1: error: unrecognized command line option "-Wno-unused-but-set-variable"

Approved by:	portmgr (tier-2 blanket)

graphics/py-gphoto2/Makefile

@@ -14,11 +14,9 @@ COMMENT=	Python bindings for libgphoto2
 LICENSE=	GPLv3+
 LICENSE_FILE=	${WRKSRC}/LICENSE.txt
 
-BROKEN_powerpc64=	fails to compile: unrecognized command line option "-Wno-unused-but-set-variable"
-
 LIB_DEPENDS=	libgphoto2.so:graphics/libgphoto2
 
-USES=		pkgconfig python shebangfix
+USES=		compiler pkgconfig python shebangfix
 USE_PYTHON=	autoplist concurrent distutils
 SHEBANG_FILES=	examples/*.py
 
@@ -30,4 +28,10 @@ post-patch:
 		-e 's|share/python-gphoto2|${DOCSDIR:S,${PREFIX}/,,}|' \
 		${WRKSRC}/setup.py
 
-.include <bsd.port.mk>
+.include <bsd.port.pre.mk>
+
+.if ${CHOSEN_COMPILER_TYPE} == gcc
+EXTRA_PATCHES=	${FILESDIR}/extra-patch-setup.py
+.endif
+
+.include <bsd.port.post.mk>

graphics/py-gphoto2/files/extra-patch-setup.py

@@ -0,0 +1,11 @@
+--- setup.py.orig	2018-01-02 11:44:51 UTC
++++ setup.py
+@@ -83,7 +83,7 @@ mod_src_dir = os.path.join(
+     'src', mod_src_dir + '-gp' + '.'.join(map(str, best_match)))
+ 
+ extra_compile_args = [
+-    '-O3', '-Wno-unused-variable', '-Wno-unused-but-set-variable',
++    '-O3', '-Wno-unused-variable',
+     '-Wno-unused-label', '-Wno-strict-prototypes',
+     '-DGPHOTO2_VERSION=' + '0x{:02x}{:02x}{:02x}'.format(*gphoto2_version)]
+ if 'PYTHON_GPHOTO2_STRICT' in os.environ: