AArch64: Add arm64 runtime support.

Adds support for arm64 to ART. Assembler stubs are sufficient for
down calls into interpreter. JNI compiler and generics are not finished.

Basic Generic JNI functionality.

Change-Id: I4a07c79d1e037b9f5746673480e32cf456867b82
diff --git a/compiler/utils/assembler.h b/compiler/utils/assembler.h
index f02c20f..cd4fc12 100644
--- a/compiler/utils/assembler.h
+++ b/compiler/utils/assembler.h
@@ -38,6 +38,9 @@
 namespace arm {
   class ArmAssembler;
 }
+namespace arm64 {
+  class Arm64Assembler;
+}
 namespace mips {
   class MipsAssembler;
 }