Add the ability to limit "source regexp" breakpoints to a particular function

within a source file.

This isn't done, I need to make the name match smarter (right now it requires an
exact match which is annoying for methods of a class in a namespace.

Also, though we use it in tests all over the place, it doesn't look like we have
a test for Source Regexp breakpoints by themselves, I'll add that in a follow-on patch.

llvm-svn: 267834