Make compiler/utils/ symbols hidden.

Test: m test-art-host-gtest
Test: testrunner.py --host --optimizing
Change-Id: I5e39375f16e0ff1372c35fda444a4ef33bf320bf
diff --git a/compiler/utils/jni_macro_assembler.h b/compiler/utils/jni_macro_assembler.h
index a91176c..79dd987 100644
--- a/compiler/utils/jni_macro_assembler.h
+++ b/compiler/utils/jni_macro_assembler.h
@@ -30,7 +30,7 @@
 #include "managed_register.h"
 #include "offsets.h"
 
-namespace art {
+namespace art HIDDEN {
 
 class ArenaAllocator;
 class DebugFrameOpCodeWriterForAssembler;