Set `copt` for internal tools like `make` and `pkgconfig`

Please add some way to pass compiler flags for building the rules_foreign_cc internal tools.

We want to build our own code base with `-Werror` but we don't have a way to disable warnings for those external tool we don't have control over.

Start by locating the rules_foreign_cc entry points that build the internal tools named in the issue, especially make and pkgconfig, and trace how copt is handled. Verify behavior by building those tools with -Werror and supplied compiler flags; done means users can control the internal tools' flags without changing their own code's flags.

Written by the indexing model from the issue text.