Test the PGO/BOLT/LTO optimized x64 Linux compiler on CI

src/bootstrap/lib.rs

@@ -222,6 +222,7 @@ pub struct Build {
     initial_cargo: PathBuf,
     initial_lld: PathBuf,
     initial_libdir: PathBuf,
+    initial_sysroot: PathBuf,
 
     // Runtime state filled in later on
     // C/C++ compilers and archiver for all targets
@@ -389,13 +390,16 @@ impl Build {
             "/dummy".to_string()
         } else {
             output(Command::new(&config.initial_rustc).arg("--print").arg("sysroot"))
-        };
+        }
+        .trim()
+        .to_string();
+
         let initial_libdir = initial_target_dir
             .parent()
             .unwrap()
             .parent()
             .unwrap()
-            .strip_prefix(initial_sysroot.trim())
+            .strip_prefix(&initial_sysroot)
             .unwrap()
             .to_path_buf();
 
@@ -425,6 +429,7 @@ impl Build {
             initial_cargo: config.initial_cargo.clone(),
             initial_lld,
             initial_libdir,
+            initial_sysroot: initial_sysroot.into(),
             local_rebuild: config.local_rebuild,
             fail_fast: config.cmd.fail_fast(),
             doc_tests: config.cmd.doc_tests(),

src/bootstrap/test.rs

@@ -1424,7 +1424,15 @@ note: if you're sure you want to do this, please open an issue as to why. In the
 
         cmd.arg("--src-base").arg(builder.src.join("tests").join(suite));
         cmd.arg("--build-base").arg(testdir(builder, compiler.host).join(suite));
-        cmd.arg("--sysroot-base").arg(builder.sysroot(compiler));
+
+        // When top stage is 0, that means that we're testing an externally provided compiler.
+        // In that case we need to use its specific sysroot for tests to pass.
+        let sysroot = if builder.top_stage == 0 {
+            builder.initial_sysroot.clone()
+        } else {
+            builder.sysroot(compiler).to_path_buf()
+        };
+        cmd.arg("--sysroot-base").arg(sysroot);
         cmd.arg("--stage-id").arg(stage_id);
         cmd.arg("--suite").arg(suite);
         cmd.arg("--mode").arg(mode);