Add wstring<->string conversion compat shim.

[benvanik]

GCC's stdlib doesn't have codecvt, while clang and msvc do. Currently this is hacked to just truncate wstring, but that's not right and should be fixed using linux-specific APIs (until GCC gets its shit together): string.cc

[PlasmaPower]

It looks like libiconv is the best choice for this. However, it is LGPG (source "The libiconv and libcharset libraries and their header files are under LGPL."). I'm not sure if it is too complicated (?), the documentation on that in CONTRIBUTING.md looks like it was not completed.

[benvanik]

We wouldn't ship the source or headers, but could rely on them being installed (apt-get install libconv...). Could have xenia-build verify its installed in its setup command (with dpkg-query or something).

[PlasmaPower]

That is what I was expecting, but I'm no expert in licensing. I'll see if I can implement that tomorrow.

[PlasmaPower]

Side note, for checking if they are installed, I wouldn't rely on dpkg-query because a lot of systems aren't dpkg based. Just checking for the library should work (with tools like locate or whereis).

[moon-chilled]

Generally, the way this is done is with pkg-config.