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_simplifier_x86_shared.cc b/compiler/optimizing/instruction_simplifier_x86_shared.cc
index 74c5ca2..2805abb 100644
--- a/compiler/optimizing/instruction_simplifier_x86_shared.cc
+++ b/compiler/optimizing/instruction_simplifier_x86_shared.cc
@@ -14,10 +14,9 @@
  */
 
 #include "instruction_simplifier_x86_shared.h"
-
 #include "nodes_x86.h"
 
-namespace art HIDDEN {
+namespace art {
 
 bool TryCombineAndNot(HAnd* instruction) {
   DataType::Type type = instruction->GetType();