Fix a couple of bugs:

1. When we accept "#garbage" in asm-with-cpp mode, change the token kind
   of the # to unknown so that the preprocessor won't try to process it as
   a real #.  This fixes a crash on the attached example
2. Fix macro definition extents processing to handle #foo at the end of a
   macro to say the definition ends with the foo, not the #.

This is a follow-on fix to r72283, and rdar://6916026

llvm-svn: 72388