Unfortunately, the MacroResolver does not scale and we get pretty bad performances when parsing big projects.

In particular macros that are only checked for definition or are
expanded during the evaluation of an #if or #elif directive are now also
added to the list available through Document::macroUses().

The names of undefined macros that are interesting (because they're used
in an #ifdef or a defined(...)) are now available through
Document::undefinedMacroUses().

Reviewed-by: Roberto Raggi <roberto.raggi@nokia.com>

Reviewed-by: Trust Me