[M680x0] Add google/benchmark's CycleTimer support for M68K

This is a cherrypick of the upstream fix commit ffe1342 onto
`llvm/utils/benchmark` and `libcxx/utils/google-benchmark`.
This adds CycleTimer implementation for M680x0, which simply
uses `gettimeofday` same as MIPS.

Differential Review: https://reviews.llvm.org/D88868