Bring startup and syscalls

cores/arduino/build_gcc/Makefile

cores/arduino/build_gcc/debug.mk

cores/arduino/build_gcc/gcc.mk

cores/arduino/build_gcc/libarduino_arduino_zero.mk

cores/arduino/build_gcc/release.mk

cores/arduino/delay.c

cores/arduino/delay.h

cores/arduino/startup.c

cores/arduino/syscalls.c

cores/arduino/syscalls.h

cores/arduino/validation/build_gcc/Makefile

cores/arduino/validation/build_gcc/debug.mk

cores/arduino/validation/build_gcc/gcc.mk

cores/arduino/validation/build_gcc/test.mk

cores/arduino/wiring.c

cores/arduino/wiring.h