configure.ac: add build/ as macro-dir

[dilyanpalauzov]

Fixes https://bugs.php.net/bug.php?id=81637

Please backport to 7.4

[cmb69]

Thanks for the PR! However, the build fails because AC_CONFIG_MACRO_DIRS is not defined. /S

And if you want to target PHP-7.4, please rebase onto that branch, force-push, and change the base branch in GH-UI (edit title).

[dilyanpalauzov]

AC_CONFIG_MACRO_DIRS() is part of Autoconf - https://www.gnu.org/software/automake/manual/html_node/Local-Macros.html . I cannot say, why the macro is not found under these circumstances.

I want to have the change in 7.4, but once I migrate to 8.0 or 8.1 I want to have the change already there, too.

[cmb69]

I'm mostly a Windows users, so can't really comment on the autotools stuff. Maybe someone else could?

Regarding the branch: always target the lowest branch you want a change to go in. If the PR gets accepted, it will be merged upwards anyway.

[dilyanpalauzov]

Moved to #7667.