Make crashes dump mir to build dir

Author: compiler-errors

src/tools/compiletest/src/runtest.rs

@@ -2560,8 +2560,15 @@ impl<'test> TestCx<'test> {
             Assembly | Codegen => {
                 rustc.arg("-Cdebug-assertions=no");
             }
+            Crashes => {
+                let mir_dump_dir = self.get_mir_dump_dir();
+                remove_and_create_dir_all(&mir_dump_dir);
+                let mut dir_opt = "-Zdump-mir-dir=".to_string();
+                dir_opt.push_str(mir_dump_dir.to_str().unwrap());
+                rustc.arg(dir_opt);
+            }
             RunPassValgrind | Pretty | DebugInfo | Rustdoc | RustdocJson | RunMake
-            | CodegenUnits | JsDocTest | Crashes => {
+            | CodegenUnits | JsDocTest => {
                 // do not use JSON output
             }
         }