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/nodes_shared.cc b/compiler/optimizing/nodes_shared.cc
index fc28c0e..2f971b9 100644
--- a/compiler/optimizing/nodes_shared.cc
+++ b/compiler/optimizing/nodes_shared.cc
@@ -23,7 +23,7 @@
 
 #include "common_arm64.h"
 
-namespace art HIDDEN {
+namespace art {
 
 using helpers::CanFitInShifterOperand;