do not enable validate-mir for std in stage 0

Author: chenyukang

src/bootstrap/builder.rs

@@ -1871,7 +1871,7 @@ impl<'a> Builder<'a> {
             }
         }
 
-        if matches!(mode, Mode::Std) {
+        if matches!(mode, Mode::Std) && compiler.stage != 0 {
             if let Some(mir_opt_level) = self.config.rust_validate_mir_opts {
                 rustflags.arg("-Zvalidate-mir");
                 rustflags.arg(&format!("-Zmir-opt-level={}", mir_opt_level));

src/tools/compiletest/src/runtest.rs

@@ -1961,7 +1961,6 @@ impl<'test> TestCx<'test> {
                 let mut dir_opt = "-Zdump-mir-dir=".to_string();
                 dir_opt.push_str(mir_dump_dir.to_str().unwrap());
                 debug!("dir_opt: {:?}", dir_opt);
-
                 rustc.arg(dir_opt);
             }
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