tree-wide: Update to new libglnx fd APIs

This ends up a lot better IMO.  This commit is *mostly* just
`s/glnx_close_fd/glnx_autofd`, but there's also a number of hunks like:

```
-  if (self->sysroot_fd != -1)
-    {
-      (void) close (self->sysroot_fd);
-      self->sysroot_fd = -1;
-    }
+  glnx_close_fd (&self->sysroot_fd);
```

Update submodule: libglnx

Closes: #1259
Approved by: jlebon

src/libostree/ostree-repo-static-delta-compilation.c

@@ -1209,12 +1209,12 @@ ostree_repo_static_delta_generate (OstreeRepo                   *self,
   g_autoptr(GVariant) to_commit = NULL;
   const char *opt_filename;
   g_autofree char *descriptor_name = NULL;
-  glnx_fd_close int descriptor_dfd = -1;
+  glnx_autofd int descriptor_dfd = -1;
   g_autoptr(GVariant) fallback_headers = NULL;
   g_autoptr(GVariant) detached = NULL;
   gboolean inline_parts;
   guint endianness = G_BYTE_ORDER;
-  glnx_fd_close int tmp_dfd = -1;
+  glnx_autofd int tmp_dfd = -1;
   builder.parts = g_ptr_array_new_with_free_func ((GDestroyNotify)ostree_static_delta_part_builder_unref);
   builder.fallback_objects = g_ptr_array_new_with_free_func ((GDestroyNotify)g_variant_unref);