MIPS: Prefer cc-option for additions to cflags

A future change will switch as-option to use KBUILD_AFLAGS instead of
KBUILD_CFLAGS to allow clang to drop -Qunused-arguments, which may cause
issues if the flag being tested requires a flag previously added to
KBUILD_CFLAGS but not KBUILD_AFLAGS. Use cc-option for cflags additions
so that the flags are tested properly.

Signed-off-by: Nathan Chancellor <[e-mail]>
Acked-by: Thomas Bogendoerfer <[e-mail]>
Reviewed-by: Nick Desaulniers <[e-mail]>
Reviewed-by: Philippe Mathieu-Daudé <[e-mail]>
Tested-by: Linux Kernel Functional Testing <[e-mail]>
Tested-by: Anders Roxell <[e-mail]>
Signed-off-by: Masahiro Yamada <[e-mail]>

arch/mips/Makefile

···
 #
 # Avoid this by explicitly disabling that assembler behaviour.
 #
-cflags-y += $(call as-option,-Wa$(comma)-mno-fix-loongson3-llsc,)
+cflags-y += $(call cc-option,-Wa$(comma)-mno-fix-loongson3-llsc,)
 
 #
 # CPU-dependent compiler/assembler options for optimization.

arch/mips/loongson2ef/Platform

···
 # binutils does not merge support for the flag then we can revisit & remove
 # this later - for now it ensures vendor toolchains don't cause problems.
 #
-cflags-$(CONFIG_CPU_LOONGSON2EF)	+= $(call as-option,-Wa$(comma)-mno-fix-loongson3-llsc,)
+cflags-$(CONFIG_CPU_LOONGSON2EF)	+= $(call cc-option,-Wa$(comma)-mno-fix-loongson3-llsc,)
 
 # Enable the workarounds for Loongson2f
 ifdef CONFIG_CPU_LOONGSON2F_WORKAROUNDS