DSUtil: Replace inline assembler by a compiler intrinsic.

This commits works around AStyle being fool by the non-standard __asm keyword.
Fix some implicit int64 to int32 conversion.
custom_messages.iss: updated Chinese Simplified translation.
Rewritten code for auto-load subtitles and support for '_' as a separator.

Being a video file named video.ext, video_whatever.srt will now be auto-loaded.

This commit fixes #3195.