RFR: 8344802: Crash in StubRoutines::verify_mxcsr with -XX:+EnableX86ECoreOpts and -Xcheck:jni [v4]

[Volodymyr Paprotski]

> (Also see `8319429: Resetting MXCSR flags degrades ecore`) 
> 
> For performance, signaling flags (bottom 6 bits) are set by default in MXCSR. This PR fixes the Xcheck:jni comparison that is producing these copious warnings:
> 
> OpenJDK 64-Bit Server VM warning: MXCSR changed by native JNI code, use -XX:+RestoreMXCSROnJNICall
> 
> 
> **This in fact happens on both Windows _AND_ Linux.** However, _only_ on Windows there is a crash. This PR fixes the crash but I have not been able to track down the source of the crash (i.e. crash in the warn handler).

Volodymyr Paprotski has updated the pull request incrementally with one additional commit since the last revision:

  fix crash in fxrstor

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/22673/files
  - new: https://git.openjdk.org/jdk/pull/22673/files/2b15f99a..b1a712bf

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=22673&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=22673&range=02-03

  Stats: 10 lines in 1 file changed: 9 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/22673.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22673/head:pull/22673

PR: https://git.openjdk.org/jdk/pull/22673