subprojects: Temporarily avoid using wrapdb while it’s down

This should fix our CI, which is currently failing on any system which requires using the zlib subproject (typically VS systems) as wrapdb is down. Work around that by pointing our wrap file at the underlying github hosting instead.

See https://github.com/mesonbuild/meson/issues/6446#issuecomment-574241715

Signed-off-by: Philip Withnall withnall@endlessm.com