build portability

I noticed a few issues in my environment

## c++17 standard is not being applied

Maybe the current config only happens to work if the C++ compiler defaults to 17?

I had to add this to top level CMakeLists.txt:
```
set(CMAKE_CXX_STANDARD 17)
```

## `ext/google_benchmark` assumes Windows

needed to disable hard-coded lib `shlwapi` in `ext/google_benchmark/CMakeLists.txt`
