Description:
------------
"configure" warns:

./configure: line 5571: -z: command not found

The script contains wrong syntax:

 5571      -z "$php_bison_version"  && php_bison_version=0.0.0
...
 5676      -z "$php_re2c_version"  && php_re2c_version=0.0.0

The root cause is in file build/php.m4 introduced in commit https://github.com/php/php-src/commit/fe2afef36fc78c267133ddd403f48e0ee799efbc (#78750, GH-5681):

1787     [ -z "$php_bison_version" ] && php_bison_version=0.0.0
...
1852     [ -z "$php_re2c_version" ] && php_re2c_version=0.0.0

The square brackets need escaping in the m4 macro files. Directly below those lines a different syntax is used. Therefore I suggest to replace the two lines as follows:

    if test -z "$php_bison_version" ; then
      php_bison_version=0.0.0
    fi

and

    if test -z "$php_re2c_version" ; then
      php_re2c_version=0.0.0
    fi

Note that the problematic change also was back-ported to PHP 7.4 after 7.4.8 (https://github.com/php/php-src/pull/5681/commits/94c76e5e964aceb7e40fc6a15cf0ce247585c154). It should be fixed there as well before the next PHP 7.4 release.