[PATCH] Option parsing: recognize the special -- token

[Hans Wennborg]

>  We should also probably file a bug against GCC to get them to implement equivalent behavior.

I found out they already have a bug for it:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29270

On that bug, it's pointed out that the tricky bit is what to do when
we pass on arguments to cc1 and other commands. I'll have a think
about that.