x86/kconfig: Add as-instr64 macro to properly evaluate AS_WRUSS

Some instructions are only available on the 64-bit architecture.

Bi-arch compilers that default to -m32 need the explicit -m64 option
to evaluate them properly.

Fixes: 18e66b6 ("x86/shstk: Add Kconfig option for shadow stack")
Closes: https://lore.kernel.org/all/20240612-as-instr-opt-wrussq-v2-1-bd950f7eead7@gmail.com/
Reported-by: Dmitry Safonov <0x7f454c46@gmail.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Tested-by: Dmitry Safonov <0x7f454c46@gmail.com>
Link: https://lore.kernel.org/r/20240612050257.3670768-1-masahiroy@kernel.org

Author: masahir0y

arch/x86/Kconfig.assembler

@@ -36,6 +36,6 @@ config AS_VPCLMULQDQ
 	  Supported by binutils >= 2.30 and LLVM integrated assembler
 
 config AS_WRUSS
-	def_bool $(as-instr,wrussq %rax$(comma)(%rbx))
+	def_bool $(as-instr64,wrussq %rax$(comma)(%rbx))
 	help
 	  Supported by binutils >= 2.31 and LLVM integrated assembler

scripts/Kconfig.include

@@ -33,7 +33,8 @@ ld-option = $(success,$(LD) -v $(1))
 
 # $(as-instr,<instr>)
 # Return y if the assembler supports <instr>, n otherwise
-as-instr = $(success,printf "%b\n" "$(1)" | $(CC) $(CLANG_FLAGS) -Wa$(comma)--fatal-warnings -c -x assembler-with-cpp -o /dev/null -)
+as-instr = $(success,printf "%b\n" "$(1)" | $(CC) $(CLANG_FLAGS) $(2) -Wa$(comma)--fatal-warnings -c -x assembler-with-cpp -o /dev/null -)
+as-instr64 = $(as-instr,$(1),$(m64-flag))
 
 # check if $(CC) and $(LD) exist
 $(error-if,$(failure,command -v $(CC)),C compiler '$(CC)' not found)