ARM: Add r3 to clobber list when configuring stack guard
ARM: Add r3 to clobber list when configuring stack guard

If you enable HW_STACK_PROTECTION, DEBUG_OPTIMIZATIONS, and
CPU_STATS, you can get a crash when switching to the main thread
due to the r3 getting munged during a inline ASM call.  This patch
fixes that by adding r3 to the clobber list.

Fixes #12821

Signed-off-by: Andy Gross <4ba87047449f5700e8758e3b1af36e94376c2fff@linaro.org>

nashif/zephyr,finikorg/zephyr,Vudentz/zephyr,explora26/zephyr,GiulianoFranchetto/zephyr,finikorg/zephyr,ldts/zephyr,zephyrproject-rtos/zephyr,GiulianoFranchetto/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,ldts/zephyr,nashif/zephyr,GiulianoFranchetto/zephyr,finikorg/zephyr,galak/zephyr,GiulianoFranchetto/zephyr,explora26/zephyr,Vudentz/zephyr,explora26/zephyr,Vudentz/zephyr,ldts/zephyr,finikorg/zephyr,ldts/zephyr,nashif/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,GiulianoFranchetto/zephyr,ldts/zephyr,nashif/zephyr,nashif/zephyr,explora26/zephyr,explora26/zephyr,Vudentz/zephyr,galak/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,galak/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr