bsd.gcc.mk: add static keyword for USE_GCC

[novel]

Summary

A proof of concept patch that adds "static" keyword for USE_GCC. With that keyword specified, gcc is not pulled as a dependency because statically linked code does not need it.

See Also: D7223

[koobs]

I wonder if it's better to stay with :build as the argument name so it's consistent with other USES/USE_* bits, all of which don't expose implementation details in their naming, instead just defined by the 'dependency type'.

I think it's easier/more obvious for people (porters/maintainers) to know that GCC is just a build only dependency, rather than something being statically linked

[mat]

Yeah, it should be :build to be consistent.

[novel]

I'm abandoning this review, please look at the better patch that's doing the same thing: https://reviews.freebsd.org/D7223