Description:
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Documentation for the zlib says that minimal required version for zlib is 1.0.9:
http://php.net/manual/en/zlib.requirements.php

However there was an update of the zlib extension API and it now requires at least 1.2.0.4 version of zlib system library. The minimal required version is also reported in the 'configure --help' output. This affects active PHP 7.1+ versions.

Test script:
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./buildconf
./configure --help | grep zlib

Expected result:
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--with-zlib=DIR         Include ZLIB support (requires zlib >= 1.2.0.4)

Actual result:
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--with-zlib=DIR         Include ZLIB support (requires zlib >= 1.0.9)