[Patch] Mangle C __stdcall and __fastcall in clang

[Anton Korobeynikov]

> Doesn't mingw need these manglings to match the Windows C ABI?
Correct, it does need it.

Another problem, which is much more severe, is that moving mangling in
clang will force non-clang users to handle the mangling by themselves.

Also, keep in mind, that gcc on linux does support stdcall / fastcall
calling conventions, but does not mangle the stuff.

-- 
With best regards, Anton Korobeynikov
Faculty of Mathematics and Mechanics, Saint Petersburg State University