PGO for libc++ am: c74f1b6bac am: 7f4b512be0 am: 043a8e2e07

Original change: https://android-review.googlesource.com/c/platform/external/libcxx/+/1605138

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: I7bd1a009b884126486cb943b9786f6e5dc014451