[RISCV][PowerPC] Fix google/benchmark benchmark::cycleclock::Now

Cherrypick the upstream fix commit a77d5f7 onto llvm/utils/benchmark
and libcxx/utils/google-benchmark.
This fixes LLVM's 32-bit RISC-V compilation, and the issues
mentioned in https://github.com/google/benchmark/pull/955
An additional cherrypick of ecc1685 fixes some minor formatting
issues introduced by the preceding commit.

Differential Revision: https://reviews.llvm.org/D78084