gcc: Fix nativesdk builds and multilib fixes with gcc 11

In newer gcc versions the headers changed locations and our multiconfig
and nativesdk tweaks to loader paths wasn't working. The broke
buildtools-extended-tarball, particularly on arm. Update to fix this.

Ultimately we should dump the gcc specs and check for hardcoded paths.
This isn't possible quite yet as this patch doesn't fix the musl ones
as we don't use that in mutlilib or nativesdk scenarios at present.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>