Generate separate stamp files for --compare-mode=nll, and also use them. :)

Author: pnkfelix

src/tools/compiletest/src/main.rs

@@ -626,7 +626,7 @@ pub fn make_test(config: &Config, testpaths: &TestPaths) -> test::TestDescAndFn
 
     // Debugging emscripten code doesn't make sense today
     let ignore = early_props.ignore
-        || (!up_to_date(config, testpaths, &early_props) && config.compare_mode.is_none())
+        || !up_to_date(config, testpaths, &early_props)
         || (config.mode == DebugInfoGdb || config.mode == DebugInfoLldb)
             && config.target.contains("emscripten");
 
@@ -642,10 +642,15 @@ pub fn make_test(config: &Config, testpaths: &TestPaths) -> test::TestDescAndFn
 }
 
 fn stamp(config: &Config, testpaths: &TestPaths) -> PathBuf {
+    let mode_suffix = match config.compare_mode {
+        Some(ref mode) => format!("-{}", mode.to_str()),
+        None => format!(""),
+    };
     let stamp_name = format!(
-        "{}-{}.stamp",
+        "{}-{}{}.stamp",
         testpaths.file.file_name().unwrap().to_str().unwrap(),
-        config.stage_id
+        config.stage_id,
+        mode_suffix
     );
     config
         .build_base