Add C++ files

board_settings.h

config/miosix_settings.h

interfaces/atomic_ops.h

interfaces/delays.cpp

interfaces/delays.h

interfaces/endianness.h

interfaces/gpio.cpp

interfaces/gpio.h

interfaces/portability.cpp

interfaces/portability.h

kernel/error.cpp

kernel/error.h

kernel/kernel.cpp

kernel/kernel.h

kernel/queue.h

kernel/scheduler/priority/priority_scheduler_types.cpp

kernel/scheduler/priority/priority_scheduler_types.h

kernel/scheduler/sched_types.h

kernel/scheduler/scheduler.h

kernel/sync.cpp