arm64: move GCC version check for ARCH_SUPPORTS_INT128 to Kconfig

This becomes much neater in Kconfig.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Reviewed-by: Kees Cook <keescook@chromium.org>

arch/arm64/Kconfig

@@ -43,6 +43,7 @@ config ARM64
 	select ARCH_USE_QUEUED_RWLOCKS
 	select ARCH_SUPPORTS_MEMORY_FAILURE
 	select ARCH_SUPPORTS_ATOMIC_RMW
+	select ARCH_SUPPORTS_INT128 if GCC_VERSION >= 50000 || CC_IS_CLANG
 	select ARCH_SUPPORTS_NUMA_BALANCING
 	select ARCH_WANT_COMPAT_IPC_PARSE_VERSION
 	select ARCH_WANT_FRAME_POINTERS

arch/arm64/Makefile

@@ -56,12 +56,6 @@ KBUILD_AFLAGS	+= $(lseinstr) $(brokengasinst)
 KBUILD_CFLAGS	+= $(call cc-option,-mabi=lp64)
 KBUILD_AFLAGS	+= $(call cc-option,-mabi=lp64)
 
-ifeq ($(cc-name),clang)
-KBUILD_CFLAGS	+= -DCONFIG_ARCH_SUPPORTS_INT128
-else
-KBUILD_CFLAGS	+= $(call cc-ifversion, -ge, 0500, -DCONFIG_ARCH_SUPPORTS_INT128)
-endif
-
 ifeq ($(CONFIG_CPU_BIG_ENDIAN), y)
 KBUILD_CPPFLAGS	+= -mbig-endian
 CHECKFLAGS	+= -D__AARCH64EB__