make clean fails in out-of-tree builds

Make clean fails with out-of-tree builds:
```
build> ../src/configure
build> make
...
build> make clean
cd contrib/minizip && { make clean ; cd ../.. ; }
/bin/sh: line 1: cd: contrib/minizip: No such file or directory
make: *** [Makefile:373: minizip-clean] Error 1
```

Is this not supported anymore?