Make compiler/debug/ symbols hidden.

And mark required symbols with EXPORT.

Test: m test-art-host-gtest
Test: testrunner.py --host --optimizing
Change-Id: I8efec9299bdd6becf625e7a59c75cbaf053eadb9
diff --git a/compiler/debug/elf_debug_line_writer.h b/compiler/debug/elf_debug_line_writer.h
index 7df301a..4896bc1 100644
--- a/compiler/debug/elf_debug_line_writer.h
+++ b/compiler/debug/elf_debug_line_writer.h
@@ -20,6 +20,7 @@
 #include <unordered_set>
 #include <vector>
 
+#include "base/macros.h"
 #include "debug/elf_compilation_unit.h"
 #include "debug/src_map_elem.h"
 #include "dex/dex_file-inl.h"
@@ -29,7 +30,7 @@
 #include "oat_file.h"
 #include "stack_map.h"
 
-namespace art {
+namespace art HIDDEN {
 namespace debug {
 
 using PositionInfos = std::vector<DexFile::PositionInfo>;