tests: fix stdin-rustc

Author: jieyouxu

tests/run-make/stdin-rustc/rmake.rs

@@ -2,7 +2,7 @@
 
 use std::path::PathBuf;
 
-use run_make_support::{is_windows, rustc};
+use run_make_support::{bin_name, is_windows, rustc};
 
 const HELLO_WORLD: &str = r#"
 fn main() {
@@ -15,11 +15,7 @@ const NOT_UTF8: &[u8] = &[0xff, 0xff, 0xff];
 fn main() {
     // echo $HELLO_WORLD | rustc -
     rustc().arg("-").stdin_buf(HELLO_WORLD).run();
-    assert!(
-        PathBuf::from(if !is_windows() { "rust_out" } else { "rust_out.exe" })
-            .try_exists()
-            .unwrap()
-    );
+    assert!(bin_name("rust_out").exists());
 
     // echo $NOT_UTF8 | rustc -
     rustc().arg("-").stdin_buf(NOT_UTF8).run_fail().assert_stderr_contains(