cross-*: restrict building only on native builds.

srcpkgs/cross-mipsel-softfloat-linux-gnu/template

@@ -34,6 +34,10 @@ makedepends="zlib-devel gmp-devel mpfr-devel libmpc-devel"
 depends="${pkgname}-libc-${version}_${revision}"
 nostrip_files="libgcc.a libgcov.a libgcc_eh.a"
 
+if [ "$CROSS_BUILD" ]; then
+	msg_error "${pkgname}-${version}: cannot be cross compiled.\n"
+fi
+
 _apply_patch() {
 	local pname="$(basename $1)"