Add riscv and attributes to Clightgen

exportclight/Clightgen.ml

@@ -185,8 +185,12 @@ let _ =
                      if Configuration.abi = "macosx"
                      then Machine.x86_32_macosx
                      else Machine.x86_32
+    | "riscV"   -> if Configuration.model = "64"
+                   then Machine.rv64
+                   else Machine.rv32
     | _         -> assert false
     end;
   Builtins.set C2C.builtins;
+  Cutil.declare_attributes C2C.attributes;
   CPragmas.initialize();
   parse_cmdline cmdline_actions