Use rust_out.exe for doctests on Windows

Author: workingjubilee

src/librustdoc/doctest.rs

@@ -310,7 +310,12 @@ fn run_test(
     let (test, line_offset, supports_color) =
         make_test(test, Some(crate_name), lang_string.test_harness, opts, edition, Some(test_id));
 
-    let output_file = outdir.path().join("rust_out");
+    // Make sure we emit well-formed executable names for our platform.
+    #[cfg(windows)]
+    let out_name = "rust_out.exe";
+    #[cfg(not(windows))]
+    let out_name = "rust_out";
+    let output_file = outdir.path().join(out_name);
 
     let rustc_binary = rustdoc_options
         .test_builder