Convert enum values to number for LuaJIT 2.0.5 compat

kiwi.lua

@@ -871,7 +871,8 @@ do
    function kiwi.error_mask(kinds, invert)
       local mask = 0
       for _, k in ipairs(kinds) do
-         mask = bor(mask, lshift(1, kiwi.ErrKind(k)))
+         -- must use tonumber only for LuaJIT 2.0 compatibility
+         mask = bor(mask, lshift(1, tonumber(kiwi.ErrKind(k)) --[[@as integer]]))
       end
       return invert and bit.bnot(mask) or mask
    end
@@ -940,8 +941,9 @@ do
          end
          local errdata = new_error(kind, message, solver, item)
          local error_mask = solver and solver.error_mask_ or 0
+         -- tonumber only required for LuaJIT 2.0 compatibility
          return item,
-            band(error_mask, lshift(1, kind --[[@as integer]])) == 0 and error(errdata)
+            band(error_mask, lshift(1, tonumber(kind) --[[@as integer]])) == 0 and error(errdata)
                or errdata
       end
       return item