bootstrap: don't install llvm-tools when it's externally provided

fixes #109194

Author: filnet

src/bootstrap/install.rs

@@ -209,7 +209,7 @@ install!((self, builder, _config),
             );
         }
     };
-    LlvmTools, alias = "llvm-tools", Self::should_build(_config), only_hosts: true, {
+    LlvmTools, alias = "llvm-tools", should_build_llvm(_config), only_hosts: true, {
         let tarball = builder
             .ensure(dist::LlvmTools { target: self.target })
             .expect("missing llvm-tools");
@@ -251,6 +251,11 @@ install!((self, builder, _config),
     };
 );
 
+fn should_build_llvm(config: &Config) -> bool {
+    // additionaly check that llvm is not externally provided
+    LlvmTools::should_build(config) && config.is_rust_llvm(config.build)
+}
+
 #[derive(Debug, Copy, Clone, Hash, PartialEq, Eq)]
 pub struct Src {
     pub stage: u32,