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/ssa_liveness_analysis.cc b/compiler/optimizing/ssa_liveness_analysis.cc
index 309d9f9..7b2c3a9 100644
--- a/compiler/optimizing/ssa_liveness_analysis.cc
+++ b/compiler/optimizing/ssa_liveness_analysis.cc
@@ -21,7 +21,7 @@
 #include "linear_order.h"
 #include "nodes.h"
 
-namespace art HIDDEN {
+namespace art {
 
 void SsaLivenessAnalysis::Analyze() {
   // Compute the linear order directly in the graph's data structure