RFR: 8295159: DSO created with -ffast-math breaks Java floating-point arithmetic [v13]

[Andrew Haley]

> A bug in GCC causes shared libraries linked with -ffast-math to disable denormal arithmetic. This breaks Java's floating-point semantics.
> 
> The bug is https://gcc.gnu.org/bugzilla/show_bug.cgi?id=55522
> 
> One solution is to save and restore the floating-point control word around System.loadLibrary(). This isn't perfect, because some shared library might load another shared library at runtime, but it's a lot better than what we do now. 
> 
> However, this fix is not complete. `dlopen()` is called from many places in the JDK. I guess the best thing to do is find and wrap them all. I'd like to hear people's opinions.

Andrew Haley has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 36 commits:

 - Merge from head
 - s/Denormal/Subnormal/g
 - Review feedback
 - Merge branch 'JDK-8295159' of https://github.com/theRealAph/jdk into JDK-8295159
 - Comments only.
 - Remove change to RestoreMXCSROnJNICalls
 - Review feedback
 - Add TestDenormalDouble.java
 - Merge branch 'JDK-8295159' of https://github.com/theRealAph/jdk into JDK-8295159
 - Fix LLVM
 - ... and 26 more: https://git.openjdk.org/jdk/compare/3cea892b...393a4384

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Changes: https://git.openjdk.org/jdk/pull/10661/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10661&range=12
  Stats: 286 lines in 10 files changed: 284 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/10661.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/10661/head:pull/10661

PR: https://git.openjdk.org/jdk/pull/10661