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
```

2020/endoh2/Makefile

@@ -86,7 +86,7 @@ ifeq ($(CC),clang)
 CSILENCE+= -Wno-comma -Wno-conversion -Wno-documentation -Wno-double-promotion \
 	-Wno-missing-prototypes -Wno-missing-variable-declarations \
 	-Wno-poison-system-directories -Wno-redundant-parens -Wno-shadow \
-	-Wno-sign-conversion
+	-Wno-sign-conversion -Wno-declaration-after-statement
 #
 CWARN+= -Weverything
 #