vircgroup: include system headers only on linux

All the system headers are used only if we are compiling on linux
and they all are present otherwise we would have seen build errors
because in our tests/vircgrouptest.c we use only __linux__ to check
whether to skip the cgroup tests or not.
Reviewed-by: NJán Tomko <jtomko@redhat.com>
Signed-off-by: NPavel Hrdina <phrdina@redhat.com>

src/util/vircgroup.c

@@ -23,24 +23,23 @@
  */
 #include <config.h>
 
-#if defined HAVE_MNTENT_H && defined HAVE_SYS_MOUNT_H \
-    && defined HAVE_GETMNTENT_R
+#ifdef __linux__
 # include <mntent.h>
 # include <sys/mount.h>
-#endif
-#include <fcntl.h>
-#include <sys/stat.h>
-
-#ifdef MAJOR_IN_MKDEV
-# include <sys/mkdev.h>
-#elif MAJOR_IN_SYSMACROS
-# include <sys/sysmacros.h>
-#endif
-
-#include <sys/types.h>
-#include <signal.h>
-#include <dirent.h>
-#include <unistd.h>
+# include <fcntl.h>
+# include <sys/stat.h>
+
+# ifdef MAJOR_IN_MKDEV
+#  include <sys/mkdev.h>
+# elif MAJOR_IN_SYSMACROS
+#  include <sys/sysmacros.h>
+# endif
+
+# include <sys/types.h>
+# include <signal.h>
+# include <dirent.h>
+# include <unistd.h>
+#endif /* __linux__ */
 
 #define __VIR_CGROUP_ALLOW_INCLUDE_PRIV_H__
 #include "vircgrouppriv.h"