ART: Factor out gAborting

Cut dependencies on base/logging.h by moving gAborting to its
own header. Leave the static storage in logging.cc.

Test: m
Change-Id: Ib2ca880e15f9cb50cb9aab803784826bb46efb5e
diff --git a/runtime/thread_list.cc b/runtime/thread_list.cc
index 9f55314..8754819 100644
--- a/runtime/thread_list.cc
+++ b/runtime/thread_list.cc
@@ -28,6 +28,7 @@
 #include "nativehelper/scoped_local_ref.h"
 #include "nativehelper/scoped_utf_chars.h"
 
+#include "base/aborting.h"
 #include "base/histogram-inl.h"
 #include "base/mutex-inl.h"
 #include "base/systrace.h"