cortex_m: Add debug symbols for OpenOCD/GDB thread support

boards/airfy-beacon/dist/openocd.cfg

boards/ek-lm4f120xl/dist/openocd.cfg

boards/fox/dist/openocd.cfg

boards/frdm-k64f/dist/openocd.cfg

boards/iotlab-a8-m3/dist/openocd.cfg

boards/iotlab-m3/dist/openocd.cfg

boards/limifrog-v1/dist/openocd.cfg

boards/msbiot/dist/openocd.cfg

boards/nucleo-f072/dist/openocd.cfg

boards/nucleo-f091/dist/openocd.cfg

boards/nucleo-f103/dist/openocd.cfg

boards/nucleo-f303/dist/openocd.cfg

boards/nucleo-f334/dist/openocd.cfg

boards/nucleo-f401/dist/openocd.cfg

boards/nucleo-l1/dist/openocd.cfg

boards/pba-d-01-kw2x/dist/openocd.cfg

boards/saml21-xpro/dist/openocd.cfg

boards/samr21-xpro/dist/openocd.cfg

boards/stm32f0discovery/dist/openocd.cfg

boards/stm32f3discovery/dist/openocd.cfg