[clang][arm64] Disable -Wasm-operand-widths warning

Clang incorrectly diagnoses msr operations as need a 64-bit operand even
if the underlying register is actually 32 bits. Silence this warning.
There are quite a few occurences of this warning so I opted to add the
-Wno-flag instead of wrapping all callsites in
`#pragma clang diagnostic ignored -Wasm-operand-widths`.

arch/arm64/rules.mk

@@ -96,6 +96,12 @@ ARCH_COMPILEFLAGS += -fno-omit-frame-pointer
 ARCH_COMPILEFLAGS_NOFLOAT := -mgeneral-regs-only
 ARCH_COMPILEFLAGS_FLOAT :=
 
+# Clang incorrectly diagnoses msr operations as need a 64-bit operand even if
+# the underlying register is actually 32 bits. Silence this warning.
+ifeq ($(call is_warning_flag_supported,-Wasm-operand-widths),yes)
+ARCH_COMPILEFLAGS += -Wno-asm-operand-widths
+endif
+
 ARCH_LDFLAGS += -z max-page-size=4096
 
 LIBGCC := $(shell $(TOOLCHAIN_PREFIX)gcc $(GLOBAL_COMPILEFLAGS) $(ARCH_COMPILEFLAGS) -print-libgcc-file-name)