the `std::filesystem::create_directories` can fail due to insufficient
permissions. We convert this error into a `SysError` and catch it
wherever required.
The implementation of `nix::createDirs` allows it to be a simple wrapper
around `std::filesystem::create_directories` as its return value is not
used anywhere.
At this point many features are stripped out, but this works:
- Can run libnix{util,store,expr} unit tests
- Can run some Nix commands
Co-Authored-By volth <volth@volth.com>
Co-Authored-By Brian McKenna <brian@brianmckenna.org>
