make build verbose

[maxbachmann]

when building as verbose using pip install -v it would be helpful, if scikit-build would set the VERBOSE environment variable. This would help in debugging broken builds, by printing e.g. the compiler arguments.

[henryiii]

I don't think we can access the number of "-v"'s, and I wouldn't want to go from nothing to showing both CMake issues and VERBOSE=1 compiler commands with just one -v. Scikit-build-core will have a configuration system & you'd be able to set verbose=true in the TOML file or by PEP 517 config options.

[henryiii]

(If we can detect the number of -v's passed, this would be fantastic, though, I think. Just think we probably can't)