silence warnings under macOS for cc, clang and gcc

Used the following script to check for warnings
not silenced via ${CSILENCE}:

```sh
find ???? -mindepth 1 -maxdepth 1 -type d | while read dir; do
(cd "$dir"; echo =-=-= "$dir" =-=-= ; csilence -v 1 clobber all ; echo ; csilence -v 1 clobber alt)
done 2>&1 | less
```

1998/fanf/Makefile

@@ -129,7 +129,7 @@ all: data ${TARGET}
 	supernova deep_magic magic charon pluto
 
 ${PROG}: ${PROG}.c
-	@echo This might take a while to complete.
+	@echo "This next step may take some time to complete:"
 	${CC} ${CFLAGS} ${PROG}.c ${LIBS} -o $@
 
 # alternative executable