Merge "Switch libcompiler_rt to the LLVM prebuilt libunwind" am: 1eda370e3c am: ec51602b49

Original change: https://android-review.googlesource.com/c/platform/external/compiler-rt/+/1554717

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: I3b7dde8734085f4d87c293b45f00671565e67c7b