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-processing.c

@@ -762,11 +762,7 @@ dispatch_set_read_source (OstreeRepo                 *repo,
   GLNX_AUTO_PREFIX_ERROR("opcode set-read-source", error);
   guint64 source_offset;
 
-  if (state->read_source_fd != -1)
-    {
-      (void) close (state->read_source_fd);
-      state->read_source_fd = -1;
-    }
+  glnx_close_fd (&state->read_source_fd);
 
   if (!read_varuint64 (state, &source_offset, error))
     return FALSE;
@@ -799,12 +795,7 @@ dispatch_unset_read_source (OstreeRepo                 *repo,
   if (state->stats_only)
     return TRUE; /* Early return */
 
-  if (state->read_source_fd != -1)
-    {
-      (void) close (state->read_source_fd);
-      state->read_source_fd = -1;
-    }
-
+  glnx_close_fd (&state->read_source_fd);
   g_clear_pointer (&state->read_source_object, g_free);
 
   return TRUE;