Switch native bridge libc to LLVM prebuilt unwinder am: 7b4fec0db9

Original change: https://android-review.googlesource.com/c/platform/frameworks/libs/native_bridge_support/+/1554766

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: I6be333af0252a6961f183b0729218ec20070b9e4