ProcessHandle implementation listing processes on AIX should use getprocs64

We see rather often failures in java/lang/ProcessHandle/TreeTest.java on AIX in TreeTest.test5.
The reason is: Previously the implementation based on the /proc file system lead to double pids in the child list; at least intermittent. Using the API getprocs64() instead I was able to eliminate those double pids (and increase the performance by a factor of 4). Otherwise we would have to add an algorithm to filter out the doubles after creating the raw list.

Here is a java callstack of the error situation:
test TreeTest.test5(): failure
java.lang.AssertionError: expected direct children expected [2] but found [3]
        at org.testng.Assert.fail(Assert.java:99)
        at org.testng.Assert.failNotEquals(Assert.java:1037)
        at org.testng.Assert.assertEqualsImpl(Assert.java:140)
        at org.testng.Assert.assertEquals(Assert.java:122)
        at org.testng.Assert.assertEquals(Assert.java:907)
        at TreeTest.test5(TreeTest.java:447)
        at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
        at java.base/java.lang.reflect.Method.invoke(Method.java:580)
        at org.testng.internal.MethodInvocationHelper.invokeMethod(MethodInvocationHelper.java:132)
        at org.testng.internal.TestInvoker.invokeMethod(TestInvoker.java:599)
        at org.testng.internal.TestInvoker.invokeTestMethod(TestInvoker.java:174)
        at org.testng.internal.MethodRunner.runInSequence(MethodRunner.java:46)
        at org.testng.internal.TestInvoker$MethodInvocationAgent.invoke(TestInvoker.java:822)
        at org.testng.internal.TestInvoker.invokeTestMethods(TestInvoker.java:147)
        at org.testng.internal.TestMethodWorker.invokeTestMethods(TestMethodWorker.java:146)
        at org.testng.internal.TestMethodWorker.run(TestMethodWorker.java:128)
        at java.base/java.util.ArrayList.forEach(ArrayList.java:1597)
        at org.testng.TestRunner.privateRun(TestRunner.java:764)
        at org.testng.TestRunner.run(TestRunner.java:585)
        at org.testng.SuiteRunner.runTest(SuiteRunner.java:384)
        at org.testng.SuiteRunner.runSequentially(SuiteRunner.java:378)
        at org.testng.SuiteRunner.privateRun(SuiteRunner.java:337)
        at org.testng.SuiteRunner.run(SuiteRunner.java:286)
        at org.testng.SuiteRunnerWorker.runSuite(SuiteRunnerWorker.java:53)
        at org.testng.SuiteRunnerWorker.run(SuiteRunnerWorker.java:96)
        at org.testng.TestNG.runSuitesSequentially(TestNG.java:1218)
        at org.testng.TestNG.runSuitesLocally(TestNG.java:1140)
        at org.testng.TestNG.runSuites(TestNG.java:1069)
        at org.testng.TestNG.run(TestNG.java:1037)
        at com.sun.javatest.regtest.agent.TestNGRunner.main(TestNGRunner.java:102)
        at com.sun.javatest.regtest.agent.TestNGRunner.main(TestNGRunner.java:58)
        at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
        at java.base/java.lang.reflect.Method.invoke(Method.java:580)
        at com.sun.javatest.regtest.agent.MainWrapper$MainTask.run(MainWrapper.java:138)
        at java.base/java.lang.Thread.run(Thread.java:1570)