Blender Git Loki

Arrempt to fix Cycles compilation with Clang

Issue is caused by missing sse flags for Clang compilers,
this flags only was set for GNU C compilers.

Added if branch for Clang now, which contains the same
flags apart from -mfpmath=sse, This is because Clang was
claiming it's unused argument.

Probably OSX would need some further checks since it's
also using Clang. I've got no idea why it could have
worked for OSX before..