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/load_store_elimination.cc b/compiler/optimizing/load_store_elimination.cc
index aa787a2..b33d0f4 100644
--- a/compiler/optimizing/load_store_elimination.cc
+++ b/compiler/optimizing/load_store_elimination.cc
@@ -70,7 +70,7 @@
  *   the special block merging structure.
  */
 
-namespace art HIDDEN {
+namespace art {
 
 // An unknown heap value. Loads with such a value in the heap location cannot be eliminated.
 // A heap location can be set to kUnknownHeapValue when: