Reduce namespace pollution.

This leaves us with just the mspace stuff and three libdex functions to clean
up. We deliberately expose the JII API, and I don't think there's anything we
can really do about the art_..._from_code stuff (and at least that starts with
"art_").

Change-Id: I77e58e8330cd2afeb496642302dfe3311e68091a
diff --git a/src/compiler/codegen/arm/armv7-a/ArchVariant.cc b/src/compiler/codegen/arm/armv7-a/ArchVariant.cc
index 609d73b..eafe5ed 100644
--- a/src/compiler/codegen/arm/armv7-a/ArchVariant.cc
+++ b/src/compiler/codegen/arm/armv7-a/ArchVariant.cc
@@ -14,6 +14,7 @@
  * limitations under the License.
  */
 
+namespace art {
 
 /*
  * Determine the initial instruction set to be used for this trace.
@@ -50,3 +51,5 @@
     dmb->defMask = ENCODE_ALL;
 #endif
 }
+
+}  // namespace art