test_fs.c: Fix issue on 32-bit systems using btrfs (#4227)

On Fedora's build system, the build environment runs on btrfs. This
revealed a bug in the test on i686 systems, where this comparison was
being performed as a comparison of two signed integers, but the
filesystem type of btrfs happens to use the higher-order bits, resulting
in it appearing as a negative value.

BTRFS_SUPER_MAGIC     0x9123683e

Signed-off-by: Stephen Gallagher <sgallagh@redhat.com>

test/test-fs.c

@@ -343,7 +343,7 @@ static void statfs_cb(uv_fs_t* req) {
   defined(__OpenBSD__) || defined(__NetBSD__)
   ASSERT_OK(stats->f_type);
 #else
-  ASSERT_GT(stats->f_type, 0);
+  ASSERT_UINT64_GT(stats->f_type, 0);
 #endif
 
   ASSERT_GT(stats->f_bsize, 0);