register is deprecated when building C++11 code and removed in C++17,
using it will cause build failures with C++ and -Werror. The register
hint keyword is likely ignored in GCC anyway.

register is deprecated when building C++11 code and removed in C++17,
using it will cause build failures with C++ and -Werror. The register
hint keyword is likely ignored in GCC anyway.

- added a centralized core implementation for all cortex CPUs
- moved default stack size defines to cpu.h in cortexm_common
- moved uart0 bufsize define to cpu.h in cortexm_common
- moved typed of panic_t to cpu.h in cortexm_common

- removed coretx-m[0|3|4]
- moved their content to cortexm_common
- adjusted cortex Makefiles to this new name
- adjusted cortex Makefiles new structure

 - Move generic implementation of atomic_set_return to core/atomic.c
 - Generic implementation of atomic compare and swap in core/atomic.c
 - atomic_cas is used to implement atomic counters in core/include/atomic.h
 - atomic_int_t is an atomic integer type
 - ATOMIC_INIT can be used as an initializer for atomic_int_t
 - ATOMIC_VALUE gets a reference to the value of an atomic integer

- removed the __attribute__((naked)) from ISRs
- removed ISR_ENTER() and ISR_EXIT() macros

Rationale: Cortex-Mx MCUs save registers R0-R4 automatically
on calling ISRs. The naked attribute tells the compiler not
to save any other registers. This is fine, as long as the
code in the ISR is not nested. If nested, it will use also
R4 and R5, which will then lead to currupted registers on
exit of the ISR. Removing the naked will fix this.

doxygen does a good job itself, identifying the unique part of the path
to identify a file.

- fixes to cortexm-common
- Added ARM CMSIS headers to cortexm_common
- thread_exit fixes to cortexm-common
- cortexm-common adjusted documentation

- cortexm_common added eINT dINT defines for now