Fix JVM test argline (#24448)

* Fix JVM test argline

The argline was being overridden by '-XX:-OmitStackTraceInFastThrow'
which led to test failures that were expecting the JVM to be in a
certain state based on the value of tests.jvm.argline but they were not
since these arguments were never passed to the JVM. Additionally, we
need to respect the provided JVM argline if it is already provided with
a flag for OmitStackTraceInFastThrow. This commit fixes this by only
setting OmitStackTraceInFastThrow if it is not already set.

* Add comment

* Fix comment

* More elaborate comment

* Sigh

buildSrc/src/main/groovy/org/elasticsearch/gradle/BuildPlugin.groovy

@@ -468,8 +468,18 @@ class BuildPlugin implements Plugin<Project> {
             File heapdumpDir = new File(project.buildDir, 'heapdump')
             heapdumpDir.mkdirs()
             jvmArg '-XX:HeapDumpPath=' + heapdumpDir
-            argLine System.getProperty('tests.jvm.argline')
-            argLine '-XX:-OmitStackTraceInFastThrow'
+            /*
+             * We only want to append -XX:-OmitStackTraceInFastThrow if a flag for OmitStackTraceInFastThrow is not already included in
+             * tests.jvm.argline.
+             */
+            final String testsJvmArgline = System.getProperty('tests.jvm.argline')
+            if (testsJvmArgline == null) {
+                argLine '-XX:-OmitStackTraceInFastThrow'
+            } else if (testsJvmArgline.indexOf("OmitStackTraceInFastThrow") < 0) {
+                argLine testsJvmArgline.trim() + ' ' + '-XX:-OmitStackTraceInFastThrow'
+            } else {
+                argLine testsJvmArgline.trim()
+            }
 
             // we use './temp' since this is per JVM and tests are forbidden from writing to CWD
             systemProperty 'java.io.tmpdir', './temp'