cgroup: don't include sys/mount.h if not needed

As cgroup implementation only works on Linux, it does not
make much sense to include sys/mount.h if other requirements are
not met, such as HAVE_MNTENT_H and HAVE_GETMNTENT_R.

Also, it fixes build on OpenBSD that requires to include sys/param.h
along with sys/mount.h.
Signed-off-by: NRoman Bogorodskiy <bogorodskiy@gmail.com>

src/util/vircgroup.c

@@ -24,10 +24,9 @@
 #include <config.h>
 
 #include <stdio.h>
-#if defined HAVE_MNTENT_H && defined HAVE_GETMNTENT_R
+#if defined HAVE_MNTENT_H && defined HAVE_SYS_MOUNT_H \
+    && defined HAVE_GETMNTENT_R
 # include <mntent.h>
-#endif
-#if defined HAVE_SYS_MOUNT_H
 # include <sys/mount.h>
 #endif
 #include <fcntl.h>