Add a predefine __WINT_UNSIGNED__, similar to __WCHAR_UNSIGNED__, and test...

Add a predefine __WINT_UNSIGNED__, similar to __WCHAR_UNSIGNED__, and test them both for ARM and X86.

Use this to fully fix Sema/format-strings.c for non-x86 platforms.

Reviewed by Chandler on IRC.

llvm-svn: 156169