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/codegen_test_utils.h b/compiler/optimizing/codegen_test_utils.h
index 470d115..dde39d4 100644
--- a/compiler/optimizing/codegen_test_utils.h
+++ b/compiler/optimizing/codegen_test_utils.h
@@ -22,7 +22,6 @@
 #include "arch/mips/registers_mips.h"
 #include "arch/mips64/registers_mips64.h"
 #include "arch/x86/registers_x86.h"
-#include "base/macros.h"
 #include "code_simulator.h"
 #include "code_simulator_container.h"
 #include "common_compiler_test.h"
@@ -54,7 +53,7 @@
 #include "code_generator_mips64.h"
 #endif
 
-namespace art HIDDEN {
+namespace art {
 
 typedef CodeGenerator* (*CreateCodegenFn)(HGraph*, const CompilerOptions&);