Fix miri tests

Author: jyn514

src/tools/miri/src/bin/miri.rs

@@ -225,7 +225,8 @@ impl rustc_driver::Callbacks for MiriCompilerCalls {
         let mut config = self.miri_config.take().expect("after_analysis must only be called once");
         // Add filename to `miri` arguments.
         let exe_path = tcx.output_filenames(()).path(OutputType::Exe);
-        config.args.insert(0, exe_path.as_path().to_string_lossy().to_string());
+        let exe_stem = exe_path.filestem().unwrap().to_string_lossy();
+        config.args.insert(0, exe_stem.to_string());
 
         // Adjust working directory for interpretation.
         if let Some(cwd) = env::var_os("MIRI_CWD") {