Test suite displays "PHP Warning: declare(encoding=...) ignored because Zend multibyte feature is turned off by settings in"

When running the test suite, there's often a message like this:

{{
PHP Warning: declare(encoding=...) ignored because Zend multibyte feature is turned off by settings in /opt/buildkit/build/crm19757.fudev.co.nz/sites/all/modules/civicrm/vendor/zetacomponents/mail/src/transports/variable/var_set.php on line 2
PHP Stack trace:
PHP 1.

() /opt/buildkit/bin/phpunit4:0
PHP 2. PHPUnit_TextUI_Command::main() /opt/buildkit/bin/phpunit4:545
PHP 3. PHPUnit_TextUI_Command->run() phar:///opt/buildkit/bin/phpunit4/phpunit/TextUI/Command.php:100
PHP 4. PHPUnit_TextUI_TestRunner->doRun() phar:///opt/buildkit/bin/phpunit4/phpunit/TextUI/Command.php:149
PHP 5. PHPUnit_Framework_TestSuite->run() phar:///opt/buildkit/bin/phpunit4/phpunit/TextUI/TestRunner.php:440
PHP 6. PHPUnit_Framework_TestCase->run() phar:///opt/buildkit/bin/phpunit4/phpunit/Framework/TestSuite.php:747
PHP 7. PHPUnit_Framework_TestResult->run() phar:///opt/buildkit/bin/phpunit4/phpunit/Framework/TestCase.php:724
PHP 8. PHPUnit_Framework_TestCase->runBare() phar:///opt/buildkit/bin/phpunit4/phpunit/Framework/TestResult.php:612
PHP 9. CiviUnitTestCase->runTest() phar:///opt/buildkit/bin/phpunit4/phpunit/Framework/TestCase.php:768
PHP 10. PHPUnit_Framework_TestCase->runTest() /opt/buildkit/build/crm19757.fudev.co.nz/sites/all/modules/civicrm/tests/phpunit/CiviTest/CiviUnitTestCase.php:184
PHP 11. ReflectionMethod->invokeArgs() phar:///opt/buildkit/bin/phpunit4/phpunit/Framework/TestCase.php:909
PHP 12. api_v3_JobProcessMailingTest->testBasic() phar:///opt/buildkit/bin/phpunit4/phpunit/Framework/TestCase.php:909
PHP 13. CiviMailUtils->assertRecipients() /opt/buildkit/build/crm19757.fudev.co.nz/sites/all/modules/civicrm/tests/phpunit/api/v3/JobProcessMailingTest.php:107
PHP 14. CiviMailUtils->getAllMessages() /opt/buildkit/build/crm19757.fudev.co.nz/sites/all/modules/civicrm/tests/phpunit/CiviTest/CiviMailUtils.php:291
PHP 15. CiviMailUtils->convertToEzc() /opt/buildkit/build/crm19757.fudev.co.nz/sites/all/modules/civicrm/tests/phpunit/CiviTest/CiviMailUtils.php:211
PHP 16. spl_autoload_call() /opt/buildkit/build/crm19757.fudev.co.nz/sites/all/modules/civicrm/tests/phpunit/CiviTest/CiviMailUtils.php:352
PHP 17. Composer\Autoload\ClassLoader->loadClass() /opt/buildkit/build/crm19757.fudev.co.nz/sites/all/modules/civicrm/tests/phpunit/CiviTest/CiviMailUtils.php:352
PHP 18. Composer\Autoload\includeFile() /opt/buildkit/build/crm19757.fudev.co.nz/sites/all/modules/civicrm/vendor/composer/ClassLoader.php:301
}}

As separately noted by Chris in StackExchange and Mollux in Github, this appears to have been fixed in newer upstream version of ezcMail:

• http://civicrm.stackexchange.com/questions/16314/does-civicrm-have-a-recommended-setting-for-zend-multibyte
• https://github.com/civicrm/zetacomponents-mail/pull/1
• https://github.com/zetacomponents/Mail/commit/da509f6f913b1af2624f75e7ac6151a0eefb00d4