RFR: 8191915: JCK tests produce incorrect results with C2

[Yangfei (Felix)]

Hi,

  Please review this 8u backport fixing a compatibility issue:

  Original bug: https://bugs.openjdk.java.net/browse/JDK-8191915 
  Original patch: http://hg.openjdk.java.net/jdk/jdk10/rev/4162f740b7bd 
  Webrev for 8u: http://cr.openjdk.java.net/~fyang/8191915-8u/webrev.00/ 

  I am using gcc-7.5 and I find this issue can always be reproduced on both aarch64 and x84_64 linux with the provided jtreg test. 
  Original patch does not apply cleanly after path shuffling, three adaptations for 8u:
  1. Adjusted copyright year update for both mathexactnode.cpp and mathexactnode.hpp;
  2. Adjusted the test command for the jtreg test in the original patch: LongMulOverflowTest.java;
  3. Removed test_mathexact.cpp in the original patch.

  Performed full jtreg test on both aarch64 and x84_64 linux. OK?

Thanks,
Felix