kbuild: remove cc-option test of -fno-stack-protector

Some Makefiles already pass -fno-stack-protector unconditionally.
For example, arch/arm64/kernel/vdso/Makefile, arch/x86/xen/Makefile.

No problem report so far about hard-coding this option. So, we can
assume all supported compilers know -fno-stack-protector.

GCC 4.8 and Clang support this option (https://godbolt.org/z/_HDGzN)

Get rid of cc-option from -fno-stack-protector.

Remove CONFIG_CC_HAS_STACKPROTECTOR_NONE, which is always 'y'.

Note:
arch/mips/vdso/Makefile adds -fno-stack-protector twice, first
unconditionally, and second conditionally. I removed the second one.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

arch/x86/mm/Makefile

@@ -22,10 +22,9 @@ obj-y				:=  init.o init_$(BITS).o fault.o ioremap.o extable.o mmap.o \
 obj-y				+= pat/
 
 # Make sure __phys_addr has no stackprotector
-nostackp := $(call cc-option, -fno-stack-protector)
-CFLAGS_physaddr.o		:= $(nostackp)
-CFLAGS_setup_nx.o		:= $(nostackp)
-CFLAGS_mem_encrypt_identity.o	:= $(nostackp)
+CFLAGS_physaddr.o		:= -fno-stack-protector
+CFLAGS_setup_nx.o		:= -fno-stack-protector
+CFLAGS_mem_encrypt_identity.o	:= -fno-stack-protector
 
 CFLAGS_fault.o := -I $(srctree)/$(src)/../include/asm/trace