doc: update BUILDING.md previous versions links

PR-URL: #52852
Reviewed-By: Richard Lau <[email protected]>
Reviewed-By: Ulises Gascón <[email protected]>
Reviewed-By: Luigi Pinca <[email protected]>
Reviewed-By: Moshe Atlow <[email protected]>
Reviewed-By: Marco Ippolito <[email protected]>
Reviewed-By: Benjamin Gruenbaum <[email protected]>

Author: targos

BUILDING.md

@@ -222,9 +222,9 @@ Supported platforms and toolchains change with each major version of Node.js.
 This document is only valid for the current major version of Node.js.
 Consult previous versions of this document for older versions of Node.js:
 
-* [Node.js 19](https://github.com/nodejs/node/blob/v19.x/BUILDING.md)
+* [Node.js 21](https://github.com/nodejs/node/blob/v21.x/BUILDING.md)
+* [Node.js 20](https://github.com/nodejs/node/blob/v20.x/BUILDING.md)
 * [Node.js 18](https://github.com/nodejs/node/blob/v18.x/BUILDING.md)
-* [Node.js 16](https://github.com/nodejs/node/blob/v16.x/BUILDING.md)
 
 ## Building Node.js on supported platforms