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/scheduler_test.cc b/compiler/optimizing/scheduler_test.cc
index 6baa2bd..4c47f2e 100644
--- a/compiler/optimizing/scheduler_test.cc
+++ b/compiler/optimizing/scheduler_test.cc
@@ -17,7 +17,6 @@
 #include "scheduler.h"
 
 #include "base/arena_allocator.h"
-#include "base/macros.h"
 #include "builder.h"
 #include "codegen_test_utils.h"
 #include "common_compiler_test.h"
@@ -35,7 +34,7 @@
 #include "scheduler_arm.h"
 #endif
 
-namespace art HIDDEN {
+namespace art {
 
 // Return all combinations of ISA and code generator that are executable on
 // hardware, or on simulator, and that we'd like to test.