bug#51457: grep - fails to compile after following steps in README-hacking

[Duncan Roe]

Hi,

I downloaded grep commit f0d97db2. Bypassed export GNULIB_SRCDIR. Did
./bootstrap, git submodule..., git commit...., ./configure and make -j17.

Got this error:
>   CC       dirname-lgpl.o
> In file included from basename-lgpl.c:25:
> ./string.h:624:5: error: token "@" is not valid in preprocessor expressions
>   624 | #if @GNULIB_FREE_POSIX@
Also:
> make[3]: *** Waiting for unfinished jobs....
> In file included from ./localeinfo.h:24,
>                  from localeinfo.c:24:
> ./wchar.h:687:5: error: token "@" is not valid in preprocessor expressions
>   687 | #if @GNULIB_FREE_POSIX@

s/@GNULIB_FREE_POSIX@/1/ in string.h and wchar.h. Now:
>   CC       malloc/dynarray_at_failure.o
> In file included from basename-lgpl.c:25:
> ./string.h:625:7: error: token "@" is not valid in preprocessor expressions
>   625 | # if (@REPLACE_FREE@ && !defined free \
Also:
> In file included from ./localeinfo.h:24,
>                  from localeinfo.c:24:
> ./wchar.h:688:7: error: token "@" is not valid in preprocessor expressions
>   688 | # if (@REPLACE_FREE@ && !defined free \

s/@REPLACE_FREE@/0/ in string.h and wchar.h. Now grep builds.

I went back to the clone and tried ./bootstrap &c. but without updating gnulib.
That builds.

Ran `git bisect` in gnulib. The problem starts with commit a4a2d039:
> Author: Paul Eggert <eggert@cs.ucla.edu>
> Date:   Tue Sep 7 17:51:39 2021 -0700
>
>     string, wchar: avoid some namespace pollution
>
>     * lib/string.in.h, lib/wchar.in.h:
>     (free): Declare by hand instead of including stdlib.h.
>     This avoids some namespace pollution.  It should also avoid some
>     nested-include problems described by Lucy Phipps in:
>     https://lists.gnu.org/r/bug-gnulib/2021-09/msg00018.html
>     * modules/string, modules/wchar:
>     (Depends-on): Add stdlib, so that REPLACE_FREE has the right value.
>     (Makefile.am): Replace @REPLACE_FREE@ when creating the include file.

Diffed with previous version but my grasp of autotools is inadequate to figure
out what needs to be done.

Over to you,

Cheers ... Duncan.