kconfig: Add support for 'as-option'

Currently kconfig does not have a feature that allows to detect if the
used assembler supports a specific compilation option.

Introduce 'as-option' to serve this purpose in the context of Kconfig:

        config X
                def_bool $(as-option,...)

Signed-off-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Acked-by: Masahiro Yamada <masahiroy@kernel.org>
Cc: linux-kbuild@vger.kernel.org
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

Author: fvincenzo

scripts/Kconfig.include

@@ -31,6 +31,12 @@ cc-option = $(success,$(CC) -Werror $(CLANG_FLAGS) $(1) -S -x c /dev/null -o /de
 # Return y if the linker supports <flag>, n otherwise
 ld-option = $(success,$(LD) -v $(1))
 
+# $(as-option,<flag>)
+# /dev/zero is used as output instead of /dev/null as some assembler cribs when
+# both input and output are same. Also both of them have same write behaviour so
+# can be easily substituted.
+as-option = $(success, $(CC) $(CLANG_FLAGS) $(1) -c -x assembler /dev/null -o /dev/zero)
+
 # $(as-instr,<instr>)
 # Return y if the assembler supports <instr>, n otherwise
 as-instr = $(success,printf "%b\n" "$(1)" | $(CC) $(CLANG_FLAGS) -c -x assembler -o /dev/null -)