RFR: 8300139 : [AIX] Use pthreads to avoid JNI_createVM call from primordial thread [v3]

[Varada M]

> 1. test/jdk/jni/nullCaller/NullCallerTest.java
> 2. test/jdk/java/lang/reflect/exeCallerAccessTest/CallerAccessTest.java
> 3. test/hotspot/jtreg/runtime/jni/CalleeSavedRegisters/FPRegs.java 
> 
>     The above tests were blocked on AIX [@require os.family != "aix"] because these tests are failing to call JNI_CreateJavaVM. This is solved by implementing JNI_CreateJavaVM call via POSIX threads. 
>    Similarly there are tests which are not blocked and still failing to call JNI_CreateJavaVM on AIX :
> 
> 4. test/hotspot/jtreg/runtime/jni/daemonDestroy/TestDaemonDestroy.java { PR : [12006](https://github.com/openjdk/jdk/pull/12006) }
> 5. test/lib-test/jdk/test/lib/process/TestNativeProcessBuilder.java 
> 
> The reported issue : [8300139](https://bugs.openjdk.org/browse/JDK-8300139l)

Varada M has updated the pull request incrementally with one additional commit since the last revision:

  Fixes

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/12302/files
  - new: https://git.openjdk.org/jdk/pull/12302/files/d106745e..87e6cfba

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12302&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12302&range=01-02

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/12302.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12302/head:pull/12302

PR: https://git.openjdk.org/jdk/pull/12302