Add tracking issue links and mention OS differences

Author: Kobzol

src/doc/src/guide/build-performance.md

@@ -86,24 +86,6 @@ Trade-offs:
 - ✅ Faster build times (both `cargo check` and `cargo build`)
 - ❌ **Requires using nightly Rust and an [unstable Rust feature][parallel-frontend-issue]**
 
-## Reducing built code
-
-### Removing unused dependencies
-
-Recommendation: Periodically review unused dependencies for removal using third-party tools like
-[cargo-machete](https://crates.io/crates/cargo-machete),
-[cargo-udeps](https://crates.io/crates/cargo-udeps),
-[cargo-shear](https://crates.io/crates/cargo-shear).
-
-When changing code,
-it can be easy to miss that a dependency is no longer used and can be removed.
-
-> *Note:* native support for this in Cargo is being tracked in [#15813](https://github.com/rust-lang/cargo/issues/15813).
-
-Trade-offs:
-- ✅ Faster full build and link times
-- ❌ May incorrectly flag dependencies as unused or miss some
-
 [parallel-frontend-blog]: https://blog.rust-lang.org/2023/11/09/parallel-rustc/
 [parallel-frontend-issue]: https://github.com/rust-lang/rust/issues/113349
 [build.rustflags]: ../reference/config.md#buildrustflags
@@ -130,8 +112,34 @@ linker = "clang"
 rustflags = ["-C", "link-arg=-fuse-ld=/path/to/mold"]
 ```
 
-> Note that since Rust `1.90.0`, the `x86_64-unknown-linux-gnu` target already defaults to the LLD linker.
-
 Trade-offs:
 - ✅ Faster link times
 - ❌ Might not support all use-cases, in particular if you depend on C or C++ dependencies
+
+The performance improvement depends a lot on your operating system:
+- On Linux, the system linker tends to be quite slow, and an alternative linker can provide a massive improvement in linking performance.
+  - Note that since Rust `1.90.0`, the `x86_64-unknown-linux-gnu` Linux target already defaults to the LLD linker.
+- On Windows, an alternative linker can somewhat help linking performance.
+- On macOS, the system linker is already very fast, and thus an alternative linker won't help much.
+
+Using an alternative linker by default is being tracked in the following issues:
+- [Using LLD by default on Windows](https://github.com/rust-lang/rust/issues/71520)
+- [Using LLD by default everywhere](https://github.com/rust-lang/rust/issues/39915)
+
+## Reducing built code
+
+### Removing unused dependencies
+
+Recommendation: Periodically review unused dependencies for removal using third-party tools like
+[cargo-machete](https://crates.io/crates/cargo-machete),
+[cargo-udeps](https://crates.io/crates/cargo-udeps),
+[cargo-shear](https://crates.io/crates/cargo-shear).
+
+When changing code,
+it can be easy to miss that a dependency is no longer used and can be removed.
+
+> *Note:* native support for this in Cargo is being tracked in [#15813](https://github.com/rust-lang/cargo/issues/15813).
+
+Trade-offs:
+- ✅ Faster full build and link times
+- ❌ May incorrectly flag dependencies as unused or miss some