Prefixed string literals

[KristofferC]

Prefixed string literals will right now emit the prefix as is:

#define S L"string"

emits

const S = L"string"

leading to an error when the file is included since no L-string macro is defined.

Perhaps the prefix can just be removed, alt a no-op L-string macro can be defined since the cconvert from the type signatures should take care of it (albeit with a copy for String -> Cwstring).

[Gnimuc]

The hard part is that libclang doesn't expose enough APIs for identifying the L-string macros.