MacOS requires a few defines that were missing from BUILD.gn.
It also requires being linked to Cocoa/IOSurface/QuartzCore.
It also needs macros to define API availability to use CAMetalLayer.

Bug: chromium:1015454
Change-Id: I6b298cc805ce1f927d2eed8f4d0e11a271f75f24
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/37628
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Tested-by: Alexis Hétu <sugoi@google.com>