Revert "Make compiler/optimizing/ symbols hidden."

This reverts commit e2727154f25e0db9a5bb92af494d8e47b181dfcf.

Reason for revert: Breaks ASAN tests (ODR violation).
Bug: 142365358

Change-Id: I38103d74a1297256c81d90872b6902ff1e9ef7a4
diff --git a/compiler/optimizing/instruction_builder.h b/compiler/optimizing/instruction_builder.h
index be1706a..d701445 100644
--- a/compiler/optimizing/instruction_builder.h
+++ b/compiler/optimizing/instruction_builder.h
@@ -18,7 +18,6 @@
 #define ART_COMPILER_OPTIMIZING_INSTRUCTION_BUILDER_H_
 
 #include "base/array_ref.h"
-#include "base/macros.h"
 #include "base/scoped_arena_allocator.h"
 #include "base/scoped_arena_containers.h"
 #include "data_type.h"
@@ -29,7 +28,7 @@
 #include "nodes.h"
 #include "quicken_info.h"
 
-namespace art HIDDEN {
+namespace art {
 
 class ArenaBitVector;
 class ArtField;