Readline 8.1 is required for bash-5.1 to work properly.
From bash-5.1 release message[1]:
> Bash can be linked against an already-installed Readline library
> rather than the private version in lib/readline if desired. Only
> readline-8.1 and later versions are able to provide all of the symbols
> that bash-5.1 requires; earlier versions of the Readline library will
> not work correctly.
[1] https://lists.gnu.org/archive/html/info-gnu/2020-12/msg00003.html
When, after patching, `configure.ac` is newer than `configure`, the
Makefile will try to regenerate `configure` from `configure.ac`.
While that might usually be desirable, in this case we want to keep
bootstrapping simple and directly use the `configure` from the package
so we can avoid a dependency on automake.
Previously, we used the `-T` parameter to automake to make sure the
timestamps were okay. However, this is brittle when we update: when the
timestamp of the original file changes, and no longer matches the
timestamp of the original file in the patch, `patch` will show a warning
but otherwise continue without updating the timestamp.
This PR changes things so we only patch `configure`, so that will always
have a newer timestamp.
We will update bash-4.4 in a separate PR (but that one has a bigger rebuild
impact so will have to target staging)
Refs #115177
