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/optimizing_unit_test.h b/compiler/optimizing/optimizing_unit_test.h
index d3229e5..e5f6941 100644
--- a/compiler/optimizing/optimizing_unit_test.h
+++ b/compiler/optimizing/optimizing_unit_test.h
@@ -20,7 +20,6 @@
 #include <memory>
 #include <vector>
 
-#include "base/macros.h"
 #include "base/malloc_arena_pool.h"
 #include "base/scoped_arena_allocator.h"
 #include "builder.h"
@@ -41,7 +40,7 @@
 
 #include "gtest/gtest.h"
 
-namespace art HIDDEN {
+namespace art {
 
 #define NUM_INSTRUCTIONS(...)  \
   (sizeof((uint16_t[]) {__VA_ARGS__}) /sizeof(uint16_t))