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/common_arm64.h b/compiler/optimizing/common_arm64.h
index e29353d..5556f16 100644
--- a/compiler/optimizing/common_arm64.h
+++ b/compiler/optimizing/common_arm64.h
@@ -17,7 +17,6 @@
 #ifndef ART_COMPILER_OPTIMIZING_COMMON_ARM64_H_
 #define ART_COMPILER_OPTIMIZING_COMMON_ARM64_H_
 
-#include "base/macros.h"
 #include "code_generator.h"
 #include "instruction_simplifier_shared.h"
 #include "locations.h"
@@ -32,7 +31,7 @@
 #include "aarch64/simulator-aarch64.h"
 #pragma GCC diagnostic pop
 
-namespace art HIDDEN {
+namespace art {
 
 using helpers::CanFitInShifterOperand;
 using helpers::HasShifterOperand;