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/code_generator_utils.h b/compiler/optimizing/code_generator_utils.h
index 2afac2f..a6b41c0 100644
--- a/compiler/optimizing/code_generator_utils.h
+++ b/compiler/optimizing/code_generator_utils.h
@@ -21,9 +21,7 @@
 #include <cstdlib>
 #include <limits>
 
-#include "base/macros.h"
-
-namespace art HIDDEN {
+namespace art {
 
 class HInstruction;