x86/build: Move '-mindirect-branch-cs-prefix' out of GCC-only block

LLVM 16 will have support for this flag so move it out of the GCC-only
block to allow LLVM builds to take advantage of it.

Signed-off-by: Nathan Chancellor <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Tested-by: Nick Desaulniers <[email protected]>
Reviewed-by: Nick Desaulniers <[email protected]>
Acked-by: Peter Zijlstra (Intel) <[email protected]>
Link: ClangBuiltLinux#1665
Link: llvm/llvm-project@6f867f9
Link: https://lore.kernel.org/r/[email protected]

Author: nathanchance

arch/x86/Makefile

@@ -14,13 +14,13 @@ endif
 
 ifdef CONFIG_CC_IS_GCC
 RETPOLINE_CFLAGS	:= $(call cc-option,-mindirect-branch=thunk-extern -mindirect-branch-register)
-RETPOLINE_CFLAGS	+= $(call cc-option,-mindirect-branch-cs-prefix)
 RETPOLINE_VDSO_CFLAGS	:= $(call cc-option,-mindirect-branch=thunk-inline -mindirect-branch-register)
 endif
 ifdef CONFIG_CC_IS_CLANG
 RETPOLINE_CFLAGS	:= -mretpoline-external-thunk
 RETPOLINE_VDSO_CFLAGS	:= -mretpoline
 endif
+RETPOLINE_CFLAGS	+= $(call cc-option,-mindirect-branch-cs-prefix)
 
 ifdef CONFIG_RETHUNK
 RETHUNK_CFLAGS		:= -mfunction-return=thunk-extern