CommandProcessor: mark some functions as static
Merge pull request #838 from Tilka/unused

CommandProcessor: mark some functions as static
DiscIO: Make the unordered set in IsSoundFile static

Doesn't need to be instantiated every time the function is called.
Merge pull request #875 from lioncash/statics

DiscIO: Make the unordered set in IsSoundFile static
PPCFP: add comment
Merge pull request #884 from FioraAeterna/ppcfpopt

PPCFP: add comment