silence compiler warnings for RHEL 9 Linux

We updated ${CSILENCE} Makefile variables for entries in an attempt to
minimize compiler warnings.  This was tested using
gcc version 11.4.1 20230605 (Red Hat 11.4.1-2) (GCC).

TODO: Recheck macOS clang to see if any new warnings have occur
      under macOS clang.

1988/applin/Makefile

@@ -39,8 +39,7 @@ include ../../var.mk
 # Common C compiler warnings to silence
 #
 CSILENCE= -Wno-expansion-to-defined -Wno-implicit-int -Wno-strict-prototypes \
-	  -Wno-gnu-line-marker
-
+	  -Wno-gnu-line-marker -Wno-return-type
 
 # Common C compiler warning flags
 #