I'm not sure that the resolution currently suggested, changing compiler.set_executables(), is the right way to go.

This change to distutils is a break of backwards compatibility. Though it is a minor change, it could still break existing code.

Fixing test.support seems just as good to me in terms of code design, and better in that it is only used internally for our tests.

(BTW, instead of `elif cmd is None or (not cmd):`, you can just use `elif not cmd:`.)