CMakeLists: Ensure we specify Unicode as the codepage on Windows

Previously we were building with MBCS, which is pretty undesirable. We
want the application to be Unicode-aware in general.

Currently, we make the command line variant of yuzu use ANSI variants of
the non-standard getopt functions that we link in for Windows, given we
only have an ANSI option-set.

We should really replace getopt with a library that we make all build
types of yuzu link in, but this will have to do for the time being.