RFR: 8295159: DSO created with -ffast-math breaks Java floating-point arithmetic [v11]

[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 incrementally with three additional commits since the last revision:

 - Review feedback
 - Merge branch 'JDK-8295159' of https://github.com/theRealAph/jdk into JDK-8295159
 - Remove change to RestoreMXCSROnJNICalls

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/10661/files
  - new: https://git.openjdk.org/jdk/pull/10661/files/a3305e5c..7cba08d0

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=10661&range=10
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=10661&range=09-10

  Stats: 30 lines in 6 files changed: 4 ins; 21 del; 5 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