emulators/qemu50: fix build on powerpc

Same fix as other qemu ports + clang goes into infinite loop, so use GCC.

emulators/qemu50/Makefile

@@ -101,7 +101,8 @@ PORTDOCS=	docs index.html interop/.buildinfo interop/* qemu-ga-ref.html qemu-ga-
 
 WITHOUT_CPU_CFLAGS=yes	#to avoid problems with register allocation
 CFLAGS:=	${CFLAGS:C/-fno-tree-vrp//}
-CFLAGS_amd64+=	-fPIC
+CFLAGS_amd64=	-fPIC
+CFLAGS_powerpc=	-D_CALL_SYSV
 CONFIGURE_ARGS=	--localstatedir=/var \
 		--extra-ldflags=-L\"${LOCALBASE}/lib\" --enable-debug \
 		--prefix=${PREFIX} --cc=${CC} --enable-netmap --enable-docs --disable-kvm \
@@ -122,6 +123,7 @@ MAKE_ARGS+=	ARCH=x86_64
 
 .if ${ARCH} == "powerpc"
 MAKE_ARGS+=	ARCH=ppc
+USE_GCC=	yes
 .endif
 
 .if ${ARCH} == "powerpc64"