Allow installation to proceed when CLT is dispersed

@benhoskings commit message should say it all. mind cutting a release with this?
Ahh I see, looks like `gcc` is installed via homebrew and is shadowing xcode tools' `gcc`.

This is the kind of situation that check is there to catch—where a suite of apps is installed, but part of it is shadowed by something else, most likely a non-matching version.

My solution would be to unlink homebrew's gcc. What do you think?