Reland "[benchmarks] Move libcxx's fork of google/benchmark and llvm/utils'""

This reverts commit e7568b68 and relands
c6f7b720.

The culprit was: missed that libc also had a dependency on one of the
copies of `google-benchmark`

Also opportunistically fixed indentation from prev. change.

Differential Revision: https://reviews.llvm.org/D112012