Adding MacroUndefined() to PPCallbacks

It is useful for users of the Preprocessor to know not only when a macro is defined, but also when it gets #undef’d.

The attached patch adds this as an additional PPCallbacks method.

-Alexei

PPCallbacks.diff (1.19 KB)

looks great, applied!
http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20090420/015956.html

Thanks,

-Chris