graphics/s2: improve experience for people on POWER newer than POWER7

Don't hardcode -mcpu.

graphics/s2/Makefile

@@ -20,7 +20,6 @@ LIB_DEPENDS=	libgtest.so:devel/googletest
 USES=		cmake compiler:c++11-lang localbase ssl
 
 CMAKE_ON=	BUILD_SHARED_LIBS
-CXXFLAGS_powerpc64=	-mcpu=power7
 USE_LDCONFIG=	yes
 
 GH_ACCOUNT=	google
@@ -38,6 +37,12 @@ GFLAGS_LIB_DEPENDS=	libgflags.so:devel/gflags
 GLOG_CMAKE_BOOL=	WITH_GLOG
 GLOG_LIB_DEPENDS=	libglog.so:devel/glog
 
+.include <bsd.port.options.mk>
+
+.if ${ARCH} == powerpc64 && !defined(CPUTYPE)
+CXXFLAGS+=	-mcpu=power7
+.endif
+
 post-install-EXAMPLES-on:
 	${MKDIR} ${STAGEDIR}${EXAMPLESDIR}
 	${INSTALL_PROGRAM} ${INSTALL_WRKSRC}/examples/point_index ${INSTALL_WRKSRC}/examples/term_index ${STAGEDIR}${EXAMPLESDIR}