- Disable unused backends and shader compilation targets.
 - Build for "arm64" to make sure ANGLE_64_BIT_CPU is defined.
 - Use a better merge command now that the branch histories are related

BUG=angleproject:2344

Change-Id: I33949e701379caacf6a392a3bb0eb3523627be14
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2090685Reviewed-by: Tim Van Patten <timvp@google.com>
Commit-Queue: Geoff Lang <geofflang@chromium.org>