Added SSE vector based mixing for platforms other than Apple that use gcc. At...

Commit by leighsmith :: r3699 /trunk/MusicKit/Frameworks/SndKit/ (6 files): (link) Added SSE vector based mixing for platforms other than Apple that use gcc. At the moment this is disabled since NSData -bytes method isn't guaranteed to return addresses which are aligned on 16 byte boundaries necessary for vector processing. This needs updating in GNUstep.