[EXPERIMENTAL] Utf8 file path supported for windows platform

[C-ColinTH]

Feature:

• Now even if the game path contains non ASCII characters, it should be able to be recognized normally.
• Even if the file name of game PK3 package and other data files contains non ASCII characters, they should still be able to load normally.

Note: Testing well on my two win10 system computers, but more samples may be needed for this.

Build: Using UTF8 flag

for example: mingw32-make ARCH=x86_64 UTF8=1