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).

1998/bas1/Makefile

@@ -42,7 +42,7 @@ CSILENCE= -Wno-bitwise-conditional-parentheses -Wno-bitwise-op-parentheses \
 	  -Wno-empty-body -Wno-invalid-source-encoding -Wno-main -Wno-parentheses \
 	  -Wno-shift-op-parentheses -Wno-deprecated-non-prototype \
 	  -Wno-implicit-int -Wno-misleading-indentation -Wno-missing-parameter-type \
-	  -Wno-return-type -Wno-unused-parameter
+	  -Wno-return-type -Wno-unused-parameter -Wno-unknown-warning-option
 
 # Common C compiler warning flags
 #