libgomp: add missing replaces for omp.h move from gcc to libgomp.

srcpkgs/gcc/libgomp.template

@@ -7,6 +7,7 @@ long_desc="${long_desc}
  for OpenMP v3.0 support."
 
 revision=2
+replaces="gcc>=4.6.3<4.6.3_3"
 
 do_install() {
 	local libmddir="usr/lib/gcc/${_triplet}/${_majorver}"