Enable rustdoc's --generate-link-to-definition for rustc docs

Author: SkiFire13

src/bootstrap/doc.rs

@@ -589,6 +589,7 @@ impl Step for Rustc {
         cargo.rustdocflag("-Zunstable-options");
         cargo.rustdocflag("-Znormalize-docs");
         cargo.rustdocflag("--show-type-layout");
+        cargo.rustdocflag("--generate-link-to-definition");
         compile::rustc_cargo(builder, &mut cargo, target);
         cargo.arg("-Zunstable-options");
         cargo.arg("-Zskip-rustdoc-fingerprint");