Re: bootstrap: improve gnulib git update logic

[Bruno Haible]

Hi Kai,

> - If we run in the "old" gnulib clone
> 
>      GNULIB_REVISION=2020-08-15 ./bootstrap
> 
>   we get the message
> 
>      fatal: reference is not a tree: 2020-08-15
> 
>   even though revision 2020-08-15 exists.  It is just not available
>   in the "old" local clone.

The patch seems to handle only the case that the user has not set
GNULIB_SRCDIR.

Shouldn't it apply also to the case with GNULIB_SRCDIR? I.e. add the new
code near this one:

  if test -d "$GNULIB_SRCDIR"/.git && test -n "$GNULIB_REVISION" \
     && ! git_modules_config submodule.gnulib.url >/dev/null; then
    (cd "$GNULIB_SRCDIR" && git checkout "$GNULIB_REVISION") || cleanup_gnulib
  fi

Bruno