Look for gzopen64 php function too for zlib detection.

Fix scenario when gzip library on latest Ubuntu LTS could not be detected breaking installation.

Example:
php > var_dump( extension_loaded( 'zlib' ) );
bool(true)
php > $f = gzopen( '/tmp/test.gz', 'r' );
Fatal error: Call to undefined function gzopen() in php shell code on line 1