Make CheckJNI and JNI workarounds mutually exclusive...

...in the opposite direction; needing workarounds turns off CheckJNI.
This isn't necessarily a good idea, but I like the cleanup parts of
this change.

Change-Id: I708235ea3e5cc35ef90b01dd810e097e3ff9dd26
diff --git a/src/java_lang_Thread.cc b/src/java_lang_Thread.cc
index 0338454..f351f20 100644
--- a/src/java_lang_Thread.cc
+++ b/src/java_lang_Thread.cc
@@ -17,6 +17,7 @@
 #include "debugger.h"
 #include "jni_internal.h"
 #include "object.h"
+#include "scoped_thread_list_lock.h"
 #include "ScopedUtfChars.h"
 #include "thread.h"
 #include "thread_list.h"