When compiling `20ecedd0b4c983bd7b88f97cd7a21461988a6c12` with GNU make (`gmake`) on FreeBSD 10.2-RELEASE, I get the following error:
```
collector/filesystem_bsd.go:60: non-bool mnt[i].f_flags & MNT_RDONLY (type C.uint64_t) used as if condition
Makefile.COMMON:85: recipe for target 'node_exporter' failed
gmake: *** [node_exporter] Error 2
```
This problem is fixed by this patch.