Add static_crt option to cpp_build::Config

[emuell]

• the option is directly passed to cc and thus behaves exactly as it does in the cc crate

Makes ugly workarounds like passing /MD as flags obsolete, which will trigger a warning as this will override the existing /MX flags initially set by the cc crate.

[ogoffart]

Thanks for the patch.
Simple enough.
The CI error is unrelated so i'll merge this anyway.

Note that there is also a From implementation from the cc::Build : https://docs.rs/cpp_build/latest/cpp_build/struct.Config.html#impl-From%3CBuild%3E-for-Config

[emuell]

Missed the From impl. That indeed would also have done the job. Thanks.

It's probably worth adding a "Config::from" constructor, which would make it more obvious in the docs?