Merge "Turn on LTO for libc++.so" am: 0860713e9e am: 8be550233c am: c29582f711

Original change: https://android-review.googlesource.com/c/platform/external/libcxx/+/2623791

Change-Id: Id73d5ad9a86e18601b6c328d48abb86a94402df6
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>