[MSVCRT] Cross build fix

[Dimitrie O. Paun]

>  When compiling with STLPort I saw a method that can eliminate the need 
> for the MSVCRT macro and yet produce MSVCRT_xxx for those who need it 
> and an xxx for those how don't.
>  Basically you have your Regular cleanroom headers-set for wine-lib and 
> external dlls. And you have another set of headers for msvcrt 
> compilation. In The second set:
> - each header does some magic like #define stat_t MSVCRT_stat_t
> - than #include <original/header.h>

This can work, one problem is that if we go this way, we'll have to 
'shadow' all symbols, or else we'll get conflict with the C library. 
In any event, it's a tricky method that can result in some strange
bugs if we don't redefine all symbols, so Alexandre will have to 
comment on it if we are to try it out.

-- 
Dimi.