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/x86_memory_gen.h b/compiler/optimizing/x86_memory_gen.h
index 1cae1a5..3f4178d 100644
--- a/compiler/optimizing/x86_memory_gen.h
+++ b/compiler/optimizing/x86_memory_gen.h
@@ -17,11 +17,10 @@
 #ifndef ART_COMPILER_OPTIMIZING_X86_MEMORY_GEN_H_
 #define ART_COMPILER_OPTIMIZING_X86_MEMORY_GEN_H_
 
-#include "base/macros.h"
 #include "nodes.h"
 #include "optimization.h"
 
-namespace art HIDDEN {
+namespace art {
 class CodeGenerator;
 
 namespace x86 {