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

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

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: Ifa673af8c4ae57e892e497c5558f05392727d460