Only install rustc-dev by default on nightly

src/tools/build-manifest/src/main.rs

@@ -474,7 +474,6 @@ impl Builder {
         // and so is rust-mingw if it's available for the target.
         components.extend(vec![
             host_component("rustc"),
-            host_component("rustc-dev"),
             host_component("rust-std"),
             host_component("cargo"),
             host_component("rust-docs"),
@@ -483,6 +482,15 @@ impl Builder {
             components.push(host_component("rust-mingw"));
         }
 
+        // The compiler libraries are not stable for end users, but `rustc-dev` was only recently
+        // split out of `rust-std`. We'll include it by default as a transition for nightly users,
+        // but ship it as an optional component on the beta and stable channels.
+        if self.rust_release == "nightly" {
+            components.push(host_component("rustc-dev"));
+        } else {
+            extensions.push(host_component("rustc-dev"));
+        }
+
         // Tools are always present in the manifest,
         // but might be marked as unavailable if they weren't built.
         extensions.extend(vec![