graphics/libglvnd: fix build on powerpc

meson.build:82:4: ERROR: Problem encountered: No ASM available for freebsd (big endian)

(cherry picked from commit 608a2f1e)

graphics/libglvnd/Makefile

@@ -33,6 +33,8 @@ CFLAGS+=	-no-integrated-as
 .elif ${ARCH} == powerpc64
 BUILD_DEPENDS=	as:devel/binutils
 CFLAGS+=	-no-integrated-as -O0
+.elif ${ARCH} == powerpc
+MESON_ARGS+=	-Dasm=disabled
 .endif
 
 # Lots of software expects gl.pc even when it can build with EGL only