RFR: [8u] JDK-8191393: Random crashes during cfree+0x1c

[Liu, Xin]

Hi,  Reviewers, 

May I request review this bugfix? 
Bug: https://bugs.openjdk.java.net/browse/JDK-8191393
Webrev: https://cr.openjdk.java.net/~xliu/8191393/webrev/

I believe that root cause  is the race condition between ConcurrentMarkThread and the VMThread.
We can’t directly backport from upstream because upstream is based on unified logging framework. further, TIP doesn’t have reentry problem while jdk8u has. 
Instead, this patch uses a mutex to protect FILE* fileStream::_file and a Boolean flag to avoid reentry.  

Of course, a mutex  is not free. Therefore, I didn't use it if users don't emit log to file. 

Test: 
I ran the stress test over 24 hours and no problem is identified. 
I passed tier1 test of jtreg. 

Thanks,
--lx