x86, cpu: disable LTO for cpu.c

Clang incorrectly inlines functions with differing stack protector
attributes, which breaks __restore_processor_state() that relies on
stack protector being disabled. This change disables LTO for cpu.c
to work aroung the bug.

Link: https://bugs.llvm.org/show_bug.cgi?id=47479Suggested-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>

arch/x86/power/Makefile

@@ -5,5 +5,9 @@ OBJECT_FILES_NON_STANDARD_hibernate_asm_$(BITS).o := y
 # itself be stack-protected
 CFLAGS_cpu.o	:= -fno-stack-protector
 
+# Clang may incorrectly inline functions with stack protector enabled into
+# __restore_processor_state(): https://bugs.llvm.org/show_bug.cgi?id=47479
+CFLAGS_REMOVE_cpu.o := $(CC_FLAGS_LTO)
+
 obj-$(CONFIG_PM_SLEEP)		+= cpu.o
 obj-$(CONFIG_HIBERNATION)	+= hibernate_$(BITS).o hibernate_asm_$(BITS).o hibernate.o