[PATCH] Fix PR bootstrap/42798

[DJ Delorie]

> That means src needs to have the config/ change before the libiberty
> patch can be applied to GCC, otherwise a build of src with
> --enable-maintainer-mode will break libiberty/configure.

You are allowed to apply libiberty patches to both gcc and src
simultaneously.  Just make sure the files end up identical (I mean
"cmp" identical) and the robomerge will be happy.

The libiberty rule is: commit to gcc or both, but not just src.