ART: Introduce NO_RETURN, Mark DoLongJump noreturn

Add NO_RETURN macro that adds C++11 noreturn attribute. Mark
DoLongJump methods as noreturn.

Change-Id: Ifde4318e370493237050d4c1349285a0382df23f
diff --git a/runtime/arch/x86/context_x86.cc b/runtime/arch/x86/context_x86.cc
index 4ea4684..52a35dd 100644
--- a/runtime/arch/x86/context_x86.cc
+++ b/runtime/arch/x86/context_x86.cc
@@ -133,6 +133,7 @@
 #else
   UNIMPLEMENTED(FATAL);
 #endif
+  UNREACHABLE();
 }
 
 }  // namespace x86