cmake: compiler: Added property flag for optimization fast

CMSIS modules dsp and nn sets the optimization flag -Ofast for their
libraries. I've now made a new compiler property optimization_fast to
avoid using ifdefs in the cmsis CMakeLists.txt files.

I've update GCC and arcmwdt (not sure if arcmwdt supports -Ofast)

Signed-off-by: Lars-Ove Karlsson <lars-ove.karlsson@iar.com>