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
```

2018/algmyr/Makefile

@@ -86,7 +86,8 @@ ifeq ($(CC),clang)
 CSILENCE+= -Wno-comma -Wno-float-conversion -Wno-float-equal -Wno-format-nonliteral \
 	-Wno-implicit-float-conversion -Wno-missing-prototypes \
 	-Wno-missing-variable-declarations -Wno-poison-system-directories \
-	-Wno-shadow -Wno-shorten-64-to-32 -Wno-sign-conversion
+	-Wno-shadow -Wno-shorten-64-to-32 -Wno-sign-conversion \
+	-Wno-declaration-after-statement
 #
 CWARN+= -Weverything
 #