swift234

Add an importer mapping for C va_list.

This is necessary on 32-bit arm, where va_list's canonical type is void*. 
Without a typedef-based mapping the importer would drop declarations used 
by the NSStringAPI bridge because they appear to have void* parameters.

This mapping does not work on x86_64. SwiftTypeConverter::VisitTypedefType() 
never sees va_list on that architecture only, perhaps due to that 
architecture's unusual definition of __builtin_va_list. The default mapping 
to COpaquePointer plus the conversion CVaListPointer=>COpaquePointer 
is still in place for that architecture. 


Swift SVN r12853