kernel: Fix gcc-9.2 warning with _StackCheckHandler

Remove FUNC_NORETURN attribute from _StackCheckHandler to address the
following warning from gcc-9.2:

kernel/compiler_stack_protect.c:62:32: error: '__stack_chk_fail'
specifies less restrictive attribute than its target
'_StackCheckHandler': 'noreturn' [-Werror=missing-attributes]

Signed-off-by: Kumar Gala <kumar.gala@linaro.org>