Fix the original bug in our diagnostic printing that got me started on

this long quest: actually use the note printing machinery for each macro
expansion note rather than a hacky version of it. This will colorize and
format the notes the same as any other. There is still some stuff to fix
here, but it's one step closer.

No test case changes because currently we don't do anything differently
that I can FileCheck for -- I don't really want to try matching the
color escape codes... Suggestions for how to test this are welcome. =]

llvm-svn: 142121