Fix: declare currentThread in startJFRRecording

Author: tajila

runtime/vm/jfr.cpp

@@ -1083,6 +1083,7 @@ BOOLEAN
 startJFRRecording(J9JavaVM *vm)
 {
 	J9HookInterface **vmHooks = getVMHookInterface(vm);
+	J9VMThread *currentThread = currentVMThread(vm);
 	BOOLEAN rc = FALSE;
 
 	Assert_VM_mustHaveVMAccess(currentThread);