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/linearize_test.cc b/compiler/optimizing/linearize_test.cc
index d5aecac..50bfe84 100644
--- a/compiler/optimizing/linearize_test.cc
+++ b/compiler/optimizing/linearize_test.cc
@@ -17,7 +17,6 @@
 #include <fstream>
 
 #include "base/arena_allocator.h"
-#include "base/macros.h"
 #include "builder.h"
 #include "code_generator.h"
 #include "dex/dex_file.h"
@@ -29,7 +28,7 @@
 #include "pretty_printer.h"
 #include "ssa_liveness_analysis.h"
 
-namespace art HIDDEN {
+namespace art {
 
 class LinearizeTest : public OptimizingUnitTest {
  protected: