Modified update.py to add arm64 for Darwin, then re-ran the script to
update the configs. Note that due to an earlier change to update.py,
this also removed the unsupported platforms from config files.

This replicates the similar change made to llvm-7 here:
https://swiftshader-review.googlesource.com/c/SwiftShader/+/46029

Bug: b/152339534
Change-Id: Ib504e54cb99f3dac03a0dd3992db678d56b1b090
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/46309Tested-by: Antonio Maiorano <amaiorano@google.com>
Kokoro-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>