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/barrier.cc b/runtime/barrier.cc
index 8d3bc0e..4329a5a 100644
--- a/runtime/barrier.cc
+++ b/runtime/barrier.cc
@@ -16,7 +16,9 @@
 
 #include "barrier.h"
 
-#include "base/logging.h"  // Required for gAborting.
+#include <android-base/logging.h>
+
+#include "base/aborting.h"
 #include "base/mutex.h"
 #include "base/time_utils.h"
 #include "thread.h"