log-bwd-multiple-msgs-stdout-stderr.phpt fails intermittently

[nikic]

I recently un-XFAILED https://github.com/php/php-src/blob/master/sapi/fpm/tests/log-bwd-multiple-msgs-stdout-stderr.phpt but it still fails intermittently with:

001+ ERROR: The actual string(16) does not match expected string(8):
002+ - EXPECT: 'msg 1 - '
003+ - ACTUAL: 'msg 1 - msg 1 - '

This looks like a genuine bug, not just a race condition. At least I don't see how we would end up with a duplicated log message.

cc @bukka

[nikic]

XFAIL restored in php/php-src@c4639a2.