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).

1985/sicherman/Makefile

@@ -42,7 +42,8 @@ CSILENCE= -Wno-comment -Wno-deprecated-non-prototype -Wno-main -Wno-pedantic \
 	  -Wno-return-type -Wno-strict-prototypes -Wno-unused-parameter \
 	  -Wno-implicit-int -Wno-implicit-function-declaration -Wno-unused-value \
 	  -Wno-multichar -Wno-uninitialized -Wno-unused-but-set-parameter \
-	  -Wno-parentheses -Wno-int-conversion -Wno-missing-parameter-type
+	  -Wno-parentheses -Wno-int-conversion -Wno-missing-parameter-type \
+	  -Wno-unknown-warning-option
 
 # Common C compiler warning flags
 #