Limit macro use tokens to the macro use range

[pgoodman]

If a macro is used in a conditional directive, e.g. #if __cplusplus >= 100, then we will mark the usage of the macro as __cplusplus >= 100 and not as __cplusplus. We can probably avoid this by making ParsedFileTracker::MacroExpands look for the end location of the macro use, then mark it somehow, e.g. in the token itself, or perhaps make ParsedFileTracker stateful, where the next time we want to inject a macro end, we already know loc we want to inject.