Correct File::Rename() with Unicode paths.

Fixes savestates in e.g. Chinese folder paths, #7235.
armjit: handle any known zero in mtc1.
Write screenshots using unicode-aware apis on win.
Create the SCREENSHOT dir using unicode as well.
Fix a Symbian compile issue.
Merge pull request #7236 from unknownbrackets/minor

Fix some Unicode path issues and tiny tweak to armjit