We should only be dealing with wcharz_t at the language boundary.
Rust callers should prefer the equivalent &wstr.
Since wcsfilecmp() is no longer exposed directly it can take &wstr only.
The original implementation without the test took me 3 hours (first time
seriously looking into this)
The functions take "wcharz_t" for smooth integration with existing C++ callers.
This is at the expense of Rust callers, which would prefer "&wstr". Would be
nice to declare a function parameter that accepts both but I don't think
that really works since "wcharz_t" drops the lifetime annotation.
