Allow mixing of thread offsets between 32 and 64bit architectures.

Begin a more full implementation x86-64 REX prefixes.
Doesn't implement 64bit thread offset support for the JNI compiler.

Change-Id: If9af2f08a1833c21ddb4b4077f9b03add1a05147
diff --git a/runtime/jni_internal.cc b/runtime/jni_internal.cc
index 13aa77f..f7aeffd 100644
--- a/runtime/jni_internal.cc
+++ b/runtime/jni_internal.cc
@@ -2829,7 +2829,7 @@
       local_ref_cookie(IRT_FIRST_SEGMENT),
       locals(kLocalsInitial, kLocalsMax, kLocal),
       check_jni(false),
-      critical(false),
+      critical(0),
       monitors("monitors", kMonitorsInitial, kMonitorsMax) {
   functions = unchecked_functions = &gJniNativeInterface;
   if (vm->check_jni) {