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/inliner.cc b/compiler/optimizing/inliner.cc
index 3b240d5..ff7ed34 100644
--- a/compiler/optimizing/inliner.cc
+++ b/compiler/optimizing/inliner.cc
@@ -47,7 +47,7 @@
 #include "ssa_phi_elimination.h"
 #include "thread.h"
 
-namespace art HIDDEN {
+namespace art {
 
 // Instruction limit to control memory.
 static constexpr size_t kMaximumNumberOfTotalInstructions = 1024;