[crac] RFR: Fix OSX x86_64 CRaC crash [v2]

[Jan Kratochvil]

> - copy-paste the same code from src/hotspot/os_cpu/linux_x86/os_linux_x86.cpp
> 
> It has fixed 3 testcases but the last 4th failure looks to be unrelated to this problem.
> 
> ==============================
> Test summary
> ==============================
>    TEST                                              TOTAL  PASS  FAIL ERROR
>    jtreg:test/jdk/jdk/crac/JarFileFactoryCacheTest/JarFileFactoryCacheTest.java
>                                                          1     1     0     0
>    jtreg:test/jdk/jdk/crac/MXBean.java                   1     1     0     0
>    jtreg:test/jdk/jdk/crac/RefQueueTest.java             1     1     0     0
>    jtreg:test/jdk/jdk/crac/recursiveCheckpoint/Test.java
>>>                                                       1     0     1     0 <<
> ==============================

Jan Kratochvil has updated the pull request incrementally with one additional commit since the last revision:

  Use nullptr
   - suggested by Radim Vansa
   - it follows upstream commit 5d1f71daf06870810c9ca24e911d6191cc4f3006

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

Changes:
  - all: https://git.openjdk.org/crac/pull/121/files
  - new: https://git.openjdk.org/crac/pull/121/files/cde36449..61f06577

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=crac&pr=121&range=01
 - incr: https://webrevs.openjdk.org/?repo=crac&pr=121&range=00-01

  Stats: 2 lines in 2 files changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/crac/pull/121.diff
  Fetch: git fetch https://git.openjdk.org/crac.git pull/121/head:pull/121

PR: https://git.openjdk.org/crac/pull/121