primitives: separating optimized functions into their own .c files.

This way we use certain compiler flags (like -msse3) only on files
containing optimized code. This avoids problems that occured when
using these flags compiling generic code and running it on platforms
that don't support these optimizations (i.e. NEON optimization on
ARM platforms).
Merge remote-tracking branch 'upstream/master'
codec/primitives: NEON now enabled for iOS
primitives: renamed NEON detection function
codec: Fixed NEON detection and incorrect RFX decoding
codec: Fixed NEON CPU detection compile issue, primitives_get race condition in rfx decoding
Merge pull request #992 from mfleisz/master

primitives: separating optimized functions into their own .c files