Use enum for read barrier options in compiler

Enums are just phenomenal. Also fixed a double load error in x86
interface check cast fast path.

Test: test-art-host

Change-Id: Iea403ce579145b6a294073f3900ad6921c1a0d53
diff --git a/compiler/optimizing/code_generator.h b/compiler/optimizing/code_generator.h
index a81f24e..bf246ad 100644
--- a/compiler/optimizing/code_generator.h
+++ b/compiler/optimizing/code_generator.h
@@ -30,6 +30,7 @@
 #include "memory_region.h"
 #include "nodes.h"
 #include "optimizing_compiler_stats.h"
+#include "read_barrier_option.h"
 #include "stack_map_stream.h"
 #include "utils/label.h"
 
@@ -50,6 +51,9 @@
 // Maximum value for a primitive long.
 static int64_t constexpr kPrimLongMax = INT64_C(0x7fffffffffffffff);
 
+static constexpr ReadBarrierOption kCompilerReadBarrierOption =
+    kEmitCompilerReadBarrier ? kWithReadBarrier : kWithoutReadBarrier;
+
 class Assembler;
 class CodeGenerator;
 class CompilerDriver;