Trying to build fat binaries for multiple arches tickles a bug [1] in
the framework detector in meson 0.50. Workaround this by not bothering
building for x86, which is probably no great loss :S
https://github.com/mesonbuild/meson/issues/5290
Install and use xorgproto, and build with optimization as clang has
warnings that only work above -O0. Also expand the build matrix for both
Xcode 8.3 and 9.2. Both images are OSX 10.12 at the moment so this is
really just a way to test with clang 8 vs 9.
Signed-off-by: Adam Jackson <ajax@redhat.com>
