wchar_t and -fshort-wchar

[Sergey Dmitrouk <sdmitrouk@accesssoftek.com>]

Hi,

musl seems to build fine with -fshort-wchar, but when client applications
are built against musl all uses of wide character literals fail due to wide
type defined internally by a compiler differs from the type of `wchar_t` in
musl headers.

I faced this on ARM where `wchar_t` is defined as `unsigned int` by
musl but it's `unsigned short` from compilers point of view.  I'd expect
similar issues with other targets.

Would it make sense to use `__WCHAR_TYPE__` for `wchar_t` when it's
available (it's already used for i386, but for different reason)?
Presumably, as compiler is responsible for creating wide literals, libc
would better agree with it on the type.

Of course, this makes sense only if you intend to support builds with
`-fshort-wchar` flag, which are not very common I believe.

Best regards,
Sergey