Make compiler/utils/ symbols hidden.

Test: m test-art-host-gtest
Test: testrunner.py --host --optimizing
Change-Id: I5e39375f16e0ff1372c35fda444a4ef33bf320bf
diff --git a/compiler/utils/x86/jni_macro_assembler_x86.cc b/compiler/utils/x86/jni_macro_assembler_x86.cc
index a1c874e..7bb167c 100644
--- a/compiler/utils/x86/jni_macro_assembler_x86.cc
+++ b/compiler/utils/x86/jni_macro_assembler_x86.cc
@@ -22,7 +22,7 @@
 #include "thread.h"
 #include "utils/assembler.h"
 
-namespace art {
+namespace art HIDDEN {
 namespace x86 {
 
 static Register GetScratchRegister() {