Fix unexpected rounding signs on OPT26-

Author: sabiwara

Diff for: lib/elixir/lib/float.ex

@@ -374,8 +374,8 @@ defmodule Float do
         case rounding do
           :ceil when sign === 0 -> 1 / power_of_10(precision)
           :floor when sign === 1 -> -1 / power_of_10(precision)
-          :ceil when sign === 1 -> -0.0
-          :half_up when sign === 1 -> -0.0
+          :ceil when sign === 1 -> minus_zero()
+          :half_up when sign === 1 -> minus_zero()
           _ -> 0.0
         end
 
@@ -406,7 +406,7 @@ defmodule Float do
 
         cond do
           num == 0 and sign == 1 ->
-            -0.0
+            minus_zero()
 
           num == 0 ->
             0.0
@@ -422,6 +422,11 @@ defmodule Float do
     end
   end
 
+  # TODO remove once we require Erlang/OTP 27+
+  # This function tricks the compiler to avoid this bug in previous versions:
+  # https://github.com/elixir-lang/elixir/blob/main/lib/elixir/lib/float.ex#L408-L412
+  defp minus_zero, do: -0.0
+
   defp decompose(significant, initial) do
     decompose(significant, 1, 0, initial)
   end