DSP: Support compiling on native posix

This commit adds support to compile cmsis-dsp
library on the host. The only definition that is
needed is `__GNUC_PYTHON__`.

When this variable is defined, all the relevant
definitions are set in the `arm_math.h` header
file. In addition, in the current commit
of cmsis library, this feature is now part
of its cmake files.
Look at: https://github.com/ARM-software/CMSIS_5/blob/659671ad826fb0a94d2b801719b1f74568378289/CMSIS/DSP/Source/configDsp.cmake



Signed-off-by: Shlomi Vaknin <shlomi.39sd@gmail.com>