xbps-src: introduce "nocross" to not allow cross compilation.

Manual.md

@@ -384,6 +384,8 @@ by all supported architectures.
 - `nostrip` If set, the ELF binaries with debugging symbols won't be stripped. By
 default all binaries are stripped.
 
+- `nocross` If set, cross compilation won't be allowed and will exit with an error.
+
 - `python_versions` A white space seperated list of python versions which will
 be used to build that package. This is only used by the `python-module` build style.
 

common/environment/setup/sourcepkg.sh

@@ -3,7 +3,7 @@
 
 ## VARIABLES
 unset -v pkgname version revision short_desc homepage license maintainer
-unset -v only_for_archs distfiles checksum build_style nonfree
+unset -v only_for_archs distfiles checksum build_style nonfree nocross
 unset -v configure_script configure_args wrksrc build_wrksrc create_wrksrc
 unset -v make_cmd make_build_args make_install_args make_build_target make_install_target python_versions
 unset -v patch_args disable_parallel_build keep_libtool_archives

common/xbps-src/shutils/common.sh

@@ -388,6 +388,9 @@ setup_pkg() {
         wrksrc="$XBPS_BUILDDIR/$wrksrc"
     fi
 
+    if [ "$cross" -a "$nocross" ]; then
+        msg_error "$pkgver: cannot be cross compiled, exiting...\n"
+    fi
 }
 
 setup_pkg_depends() {