ART: Introduce thread-current-inl.h

Factor out Thread::Current() code into its own -inl file to remove
transitive includes.

This requires at the same time correcting mutex.h, i.e., moving
some functions into mutex-inl.h.

Test: m test-art-host
Change-Id: I88f888b604e0897368d9b483edce6ce4332dd9c9
diff --git a/runtime/base/logging.cc b/runtime/base/logging.cc
index 553928d..adfd7d3 100644
--- a/runtime/base/logging.cc
+++ b/runtime/base/logging.cc
@@ -21,7 +21,7 @@
 #include <sstream>
 
 #include "base/mutex.h"
-#include "thread-inl.h"
+#include "thread-current-inl.h"
 #include "utils.h"
 
 // Headers for LogMessage::LogLine.