ART: Move read barrier config out of globals

Reduce the global dependencies by refactoring where the read
barrier constants are defined.

Rename read_barier_c.h to read_barier_config.h and ifdef the
C++ parts to have a common header for both C/asm and C++.

Put heap poisoning configuration into its own minimal header.

Fix up transitive includes.

Test: m
Change-Id: I159669ec61e3d1c4c7ddcd79e63b023a0519717a
diff --git a/runtime/read_barrier.h b/runtime/read_barrier.h
index 8a106aa..45e78bc 100644
--- a/runtime/read_barrier.h
+++ b/runtime/read_barrier.h
@@ -24,10 +24,7 @@
 #include "jni.h"
 #include "mirror/object_reference.h"
 #include "offsets.h"
-#include "read_barrier_c.h"
-
-// This is a C++ (not C) header file, separate from read_barrier_c.h
-// which needs to be a C header file for asm_support.h.
+#include "read_barrier_config.h"
 
 namespace art {
 namespace mirror {