x86: disable stack-protector for __restore_processor_state()

The __restore_processor_state() fn restores %gs on resume from S3.  As
such, it cannot be protected by the stack-protector guard since %gs will
not be correct on function entry.

There are only a few other fns in this file and it should not negatively
impact kernel security that they will also have the stack-protector
guard removed (and so it's not worth moving them to another file).

Without this change, S3 resume on a kernel built with
CONFIG_CC_STACKPROTECTOR_ALL=y will fail.

Signed-off-by: Joseph Cihula <joseph.cihula@intel.com>
Tested-by: Chris Wright <chrisw@sous-sol.org>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Tejun Heo <tj@kernel.org>
LKML-Reference: <49D13385.5060900@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/power/Makefile

@@ -1,2 +1,7 @@
+# __restore_processor_state() restores %gs after S3 resume and so should not
+# itself be stack-protected
+nostackp := $(call cc-option, -fno-stack-protector)
+CFLAGS_cpu_$(BITS).o	:= $(nostackp)
+
 obj-$(CONFIG_PM_SLEEP)		+= cpu_$(BITS).o
 obj-$(CONFIG_HIBERNATION)	+= hibernate_$(BITS).o hibernate_asm_$(BITS).o