Broaden scope of gAborting. Fixes hang in HandleUnexpectedSignal.

Change-Id: I4c29cd7b67f07bb9f99c308feac5a3d6c236bc2b
diff --git a/src/mutex.h b/src/mutex.h
index 4af2ad7..d0c6369 100644
--- a/src/mutex.h
+++ b/src/mutex.h
@@ -107,7 +107,7 @@
 
   // Assert that the Mutex is exclusively held by the current thread.
   void AssertExclusiveHeld(const Thread* self) {
-    if (kDebugLocking) {
+    if (kDebugLocking && !gAborting) {
       CHECK(IsExclusiveHeld(self)) << *this;
     }
   }