Linker warnings usually means something does not get placed where it is
supposed to and the most likely result is a broken binary.
Linker warnings should be treated as serious problems with the program
and should be solved before the program is tested on actual hardware.
- removed coretx-m[0|3|4]
- moved their content to cortexm_common
- adjusted cortex Makefiles to this new name
- adjusted cortex Makefiles new structure
