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).

1996/gandalf/Makefile

@@ -42,7 +42,7 @@ CSILENCE= -Wno-error -Wno-implicit-function-declaration -Wno-keyword-macro \
 	  -Wno-shift-op-parentheses -Wno-unused-parameter -Wno-implicit-int \
 	  -Wno-deprecated-non-prototype -Wno-strict-prototypes -Wno-unsequenced \
 	  -Wno-builtin-declaration-mismatch -Wno-parentheses -Wno-return-type \
-          -Wno-sequence-point
+          -Wno-sequence-point -Wno-unknown-warning-option
 
 # Common C compiler warning flags
 #

1996/jonth/Makefile

@@ -43,7 +43,7 @@ CSILENCE= -Wno-char-subscripts -Wno-error -Wno-implicit-function-declaration \
 	  -Wno-unsequenced -Wno-unused-parameter -Wno-deprecated-non-prototype \
 	  -Wno-builtin-declaration-mismatch -Wno-missing-parameter-type \
           -Wno-multistatement-macros -Wno-sequence-point -Wno-unused-value \
-	  -Wno-implicit-int
+	  -Wno-implicit-int -Wno-unknown-warning-option
 
 # Common C compiler warning flags
 #

1996/westley/Makefile

@@ -40,7 +40,8 @@ include ../../var.mk
 #
 CSILENCE= -Wno-char-subscripts -Wno-error -Wno-implicit-function-declaration \
 	  -Wno-int-to-pointer-cast -Wno-empty-body -Wno-deprecated-non-prototype\
-	  -Wno-implicit-int -Wno-missing-parameter-type -Wno-return-type
+	  -Wno-implicit-int -Wno-missing-parameter-type -Wno-return-type \
+	  -Wno-unknown-warning-option
 
 # Common C compiler warning flags
 #