Metal: Build built-in shaders from source on the simulator Compiling the built-in shaders with iphonesimulator sdk generates the same shaders as on iOS which do not work on the simulator. Fall back to simply building them from source on the simulator. Bug: chromium:1385510 Change-Id: If6a3846fd06a4ff12c1e46c31f207e2a7b6c50bb Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/4515521 Reviewed-by: Kenneth Russell <kbr@chromium.org> Commit-Queue: Geoff Lang <geofflang@chromium.org>