r215290 - Fix six tests are failing on Windows after r215241-r215243.

[Rafael Espíndola]

> +#ifndef LLVM_ON_WIN32
>      llvm::sys::path::native(NormalizedPath);
> +#endif

This call is used on linux to make
Lexer/cross-windows-on-linux-default.cpp pass. Since on windows both /
and \ are supposed to work, it seems that LookupFile should succeed
even with the call to llvm::sys::path::native, no? Do you know why it
is failing?

Cheers,
Rafael