compiletest: `$DIR` replacement logic misses a case on Windows

[jieyouxu]

See #134056 (comment) for example failure.

-    |     ----- ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Trait` is not implemented for closure `{closure@E:\rust\tests\ui\traits\fn-pointer\bare-fn-no-impl-fn-ptr-99875.rs:14:11: 14:34}`
+    |     ----- ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Trait` is not implemented for closure `{closure@$DIR/bare-fn-no-impl-fn-ptr-99875.rs:14:11: 14:34}`

detailed failure

---- [ui] tests\ui\traits\fn-pointer\bare-fn-no-impl-fn-ptr-99875.rs stdout ----
  $DIR\bare-fn-no-impl-fn-ptr-99875.rs
  $DIR\bare-fn-no-impl-fn-ptr-99875.rs
  $DIR\bare-fn-no-impl-fn-ptr-99875.rs
  $DIR\bare-fn-no-impl-fn-ptr-99875.rs
  $DIR\bare-fn-no-impl-fn-ptr-99875.rs
  $DIR\bare-fn-no-impl-fn-ptr-99875.rs
  Saved the actual stderr to "E:\\rust\\build\\x86_64-pc-windows-msvc\\test\\ui\\traits\\fn-pointer\\bare-fn-no-impl-fn-ptr-99875\\bare-fn-no-impl-fn-ptr-99875.stderr"
  diff of stderr:
  
  20	  --> $DIR/bare-fn-no-impl-fn-ptr-99875.rs:14:11
  21	   |
  22	LL |     takes(|_: Argument| -> Return { todo!() });
  -	   |     ----- ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unsatisfied trait bound
  +	   |     ----- ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Trait` is not implemented for closure `{closure@$DIR/bare-fn-no-impl-fn-ptr-99875.rs:14:11: 14:34}`
  24	   |     |
  25	   |     required by a bound introduced by this call
  26	   |
  
  -	   = help: the trait `Trait` is not implemented for closure `{closure@$DIR/bare-fn-no-impl-fn-ptr-99875.rs:14:11: 14:34}`
  28	   = help: the trait `Trait` is implemented for fn pointer `fn(Argument) -> Return`
  29	note: required by a bound in `takes`
  30	  --> $DIR/bare-fn-no-impl-fn-ptr-99875.rs:9:18
  
  Note: some mismatched output was normalized before being compared
  -	   |     ----- ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Trait` is not implemented for closure `{closure@E:\rust\tests\ui\traits\fn-pointer\bare-fn-no-impl-fn-ptr-99875.rs:14:11: 14:34}`
  +	   |     ----- ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Trait` is not implemented for closure `{closure@$DIR/bare-fn-no-impl-fn-ptr-99875.rs:14:11: 14:34}`
  
  
  The actual stderr differed from the expected stderr.
  To update references, rerun the tests and pass the `--bless` flag
  To only update this specific test, also pass `--test-args traits\fn-pointer\bare-fn-no-impl-fn-ptr-99875.rs`

[jieyouxu]

The closure contains a path which is not correctly handled.

Test is tests\ui\traits\fn-pointer\bare-fn-no-impl-fn-ptr-99875.rs.

[compiler-errors]

Reminds me of #132161 (comment)

[jieyouxu]

This is actually a duplicate of #132752, I forgor that existed.