RFR JDK-8026300: VM warning: increase O_BUFLEN in ostream.hpp -- output truncated occurs with fastdebug VM when printing flags

[Zhengyu Gu]

This is a simple fix in context of nightly failures cleaning up. The fix will go into JDK 9 once the repository is open.

Bug: https://bugs.openjdk.java.net/browse/JDK-8026300
Webrev:  http://cr.openjdk.java.net/~zgu/8026300/webrev.00/

Test:
  Tested on reported platform, which is Linux 32 bit.

Thanks,

-Zhengyu