add the correct version of LLVM into the stage0 sysroot

In some cases(see rust-lang#109314), when the stage0
compiler relies on more recent version of LLVM than the beta compiler, it may not
be able to locate the correct LLVM in the sysroot. This situation typically occurs
when we upgrade LLVM version while the beta compiler continues to use an older version.

Signed-off-by: ozkanonur <work@onurozkan.dev>

Author: onur-ozkan

src/bootstrap/compile.rs

@@ -1390,6 +1390,16 @@ impl Step for Sysroot {
         let _ = fs::remove_dir_all(&sysroot);
         t!(fs::create_dir_all(&sysroot));
 
+        // In some cases(see https://github.com/rust-lang/rust/issues/109314), when the stage0
+        // compiler relies on more recent version of LLVM than the beta compiler, it may not
+        // be able to locate the correct LLVM in the sysroot. This situation typically occurs
+        // when we upgrade LLVM version while the beta compiler continues to use an older version.
+        //
+        // Make sure to add the correct version of LLVM into the stage0 sysroot.
+        if compiler.stage == 0 {
+            dist::maybe_install_llvm_target(builder, compiler.host, &sysroot);
+        }
+
         // If we're downloading a compiler from CI, we can use the same compiler for all stages other than 0.
         if builder.download_rustc() && compiler.stage != 0 {
             assert_eq!(