silence compiler warnings for macOS

After silencing compiler warnings for RHEL 9 Linux,
we silence the result on macOS for
Apple clang version 15.0.0 (clang-1500.3.9.4).

1995/cdua/Makefile

@@ -92,7 +92,8 @@ ifeq "$(findstring $(CLANG),${CC})" "$(CLANG)"
 CSILENCE+= -Wno-comma -Wno-missing-variable-declarations \
 	   -Wno-poison-system-directories -Wno-strict-prototypes \
 	   -Wno-format-nonliteral -Wno-sign-conversion \
-	   -Wno-incompatible-function-pointer-types-strict -Wno-unsafe-buffer-usage
+	   -Wno-incompatible-function-pointer-types-strict -Wno-unsafe-buffer-usage \
+	   -Wno-unknown-warning-option
 #
 CWARN+= -Weverything
 #