Merge "linux_bionic_arm64 is always built from source" am: d48ce92368 am: b0123fa280 am: 1d0eff3aae am: cdaaa3f2d5

Original change: https://android-review.googlesource.com/c/platform/external/llvm/+/1409867

Change-Id: Iaac563ffffb9e24be818a2c6022295bee5235bea