check_disk - fix false DISK CRITICAL alert for btrfs filesystems due to BSD Gnulib workaround

plugins/check_disk.c

@@ -1310,10 +1310,14 @@ get_stats (struct parameter_list *p, struct fs_usage *fsp) {
 
 void
 get_path_stats (struct parameter_list *p, struct fs_usage *fsp) {
+#if defined(__NetBSD__) || defined(__FreeBSD__) || defined(OpenBSD )
   /* 2007-12-08 - Workaround for Gnulib reporting insanely high available
   * space on BSD (the actual value should be negative but fsp->fsu_bavail
   * is unsigned) */
   p->available = fsp->fsu_bavail > fsp->fsu_bfree ? 0 : fsp->fsu_bavail;
+#else
+  p->available = fsp->fsu_bavail;
+#endif
   p->available_to_root = fsp->fsu_bfree;
   p->used = fsp->fsu_blocks - fsp->fsu_bfree;
   if (freespace_ignore_reserved) {
@@ -1403,4 +1407,4 @@ human_disk_entry_comparer(const void* _lhs, const void* _rhs) {
     } else {
         return lhs->disk_result < rhs->disk_result ? 1 : -1;
     }
-}
+}