Add cross-links between feature gate docs

src/feature-gate-check.md

@@ -1,5 +1,8 @@
 # Feature Gate Checking
 
+For the how-to steps to add, remove, rename, or stabilize feature gates,
+see [Feature gates][feature-gates].
+
 Feature gates prevent usage of unstable language and library features without a
 nightly-only `#![feature(...)]` opt-in. This chapter documents the implementation
 of feature gating: where gates are defined, how they are enabled, and how usage
@@ -138,3 +141,4 @@ Diagnostic helpers are located in [`rustc_session/src/parse.rs`].
 [`rustc_attr_parsing/src/attributes/cfg.rs`]: https://github.com/rust-lang/rust/blob/HEAD/compiler/rustc_attr_parsing/src/attributes/cfg.rs
 [`rustc_feature::find_gated_cfg`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_feature/fn.find_gated_cfg.html
 [`rustc_span/src/lib.rs`]: https://github.com/rust-lang/rust/blob/HEAD/compiler/rustc_span/src/lib.rs
+[feature-gates]: ./feature-gates.md

src/feature-gates.md

@@ -3,9 +3,13 @@
 This chapter is intended to provide basic help for adding, removing, and
 modifying feature gates.
 
+For how rustc enforces and checks feature gates in the compiler pipeline,
+see [Feature Gate Checking][feature-gate-check].
+
 Note that this is specific to *language* feature gates; *library* feature gates use [a different
 mechanism][libs-gate].
 
+[feature-gate-check]: ./feature-gate-check.md
 [libs-gate]: ./stability.md
 
 ## Adding a feature gate