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/block_builder.cc b/compiler/optimizing/block_builder.cc
index 2cb2c68..a5f78ca 100644
--- a/compiler/optimizing/block_builder.cc
+++ b/compiler/optimizing/block_builder.cc
@@ -22,7 +22,7 @@
 #include "dex/dex_file_exception_helpers.h"
 #include "quicken_info.h"
 
-namespace art HIDDEN {
+namespace art {
 
 HBasicBlockBuilder::HBasicBlockBuilder(HGraph* graph,
                                        const DexFile* const dex_file,