A patch for a new callback for the preprocessor

dear cfe-dev,

while working with your preprocessor,
I found really useful to attach callbacks to events such as ChangeFile.

Now I also needed a new callback hook for the `macro expansion'
event, which seems to be missing. Hence, I am proposing the attached simple
patch.

This new feature allows me to code checkers for coding rules like
`Your program shall not use the setjmp macro'

pb

diff -u --ignore-all-space -r llvm/tools/clang/include/clang/Lex/PPCallbacks.h src/tools/clang/include/clang/Lex/PPCallbacks.h
--- llvm/tools/clang/include/clang/Lex/PPCallbacks.h. 2009-03-12 11:43:52.000000000 +0100
+++ src/tools/clang/include/clang/Lex/PPCallbacks.h.2009-03-12 16:49:21.000000000 +0100
@@ -15,6 +15,7 @@
#define LLVM_CLANG_LEX_PPCALLBACKS_H

Sure, sounds good. I committed a modified patch here:
http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20090309/013849.html

Note that this will have limited utility for function-like macros. It might be better to call the callback down lower after the MacroArgs are parsed and constructed.

-Chris