rename rustc's lld to rust-lld

to not shadow the system installed LLD when linking with LLD.

Before:

- `-C linker=lld -Z linker-flavor=ld.lld` uses rustc's LLD
- It's not possible to use a system installed LLD that's named `lld`

With this commit:

- `-C linker=rust-lld -Z linker-flavor=ld.lld` uses rustc's LLD
- `-C linker=lld -Z linker-flavor=ld.lld` uses the system installed LLD

src/bootstrap/compile.rs

@@ -786,8 +786,11 @@ fn copy_lld_to_sysroot(builder: &Builder,
         .join("bin");
     t!(fs::create_dir_all(&dst));
 
-    let exe = exe("lld", &target);
-    builder.copy(&lld_install_root.join("bin").join(&exe), &dst.join(&exe));
+    let src_exe = exe("lld", &target);
+    let dst_exe = exe("rust-lld", &target);
+    // we prepend this bin directory to the user PATH when linking Rust binaries. To
+    // avoid shadowing the system LLD we rename the LLD we provide to `rust-lld`.
+    builder.copy(&lld_install_root.join("bin").join(&src_exe), &dst.join(&dst_exe));
 }
 
 /// Cargo's output path for the standard library in a given stage, compiled

src/bootstrap/dist.rs

@@ -491,16 +491,18 @@ impl Step for Rustc {
 
             // Copy over lld if it's there
             if builder.config.lld_enabled {
-                let exe = exe("lld", &compiler.host);
+                let src_exe = exe("lld", &compiler.host);
+                let dst_exe = exe("rust-lld", &compiler.host);
                 let src = builder.sysroot_libdir(compiler, host)
                     .parent()
                     .unwrap()
                     .join("bin")
-                    .join(&exe);
+                    .join(&src_exe);
+                // for the rationale about this rename check `compile::copy_lld_to_sysroot`
                 let dst = image.join("lib/rustlib")
                     .join(&*host)
                     .join("bin")
-                    .join(&exe);
+                    .join(&dst_exe);
                 t!(fs::create_dir_all(&dst.parent().unwrap()));
                 builder.copy(&src, &dst);
             }

src/librustc_target/spec/wasm32_unknown_unknown.rs

@@ -51,6 +51,9 @@ pub fn target() -> Result<Target, String> {
         // no dynamic linking, no need for default visibility!
         default_hidden_visibility: true,
 
+        // we use the LLD shipped with the Rust toolchain by default
+        linker: Some("rust-lld".to_owned()),
+
         .. Default::default()
     };
     Ok(Target {