cc: -Xarch should not skip the next argument.

The format is -Xarch_i386 as opposed to -Xarch i386 unliked -arch i386
so the next argument should not be skipped. This was causing issues for
some formulae e.g. qt in which case it was skipping -m3dnow and -mmmx.
qt: remove superenv hacks.
Merge pull request #1 from mikemcquaid/superenv-Xarch

Superenv xarch