Then the regexp will not match.

I was about to claim that the `'gnu` regexp makes the same trade-off, but I decided to actually check that claim.  Which is good, because the claim would have been false.

(You can see that regexp with its documentation at [mirrors/emacs](https://github.com/mirrors/emacs/blob/e28072741a18e74e07d591c39953723964fc8587/lisp/progmodes/compile.el#L235).)

I'll see if I can improve upon this to support spaces as well, and in the meantime I will close this pull request.