For anyone who builds from source from a Git checkout, beware that the build system has changed. Ideally, you won't notice any difference, but there are bound to be some problems in the next few days and weeks.
The change involves replacing most of the old makefiles with new build scripts. The new scripts use a Racket-like language (GitHub - racket/zuo: A tiny Racket for scripting) that builds especially easily, so it can be used to build Racket. Makefiles and configure scripts still serve as the main points to start a Racket build, so you can still use make and configure as before. The makefiles mostly just ensure that zuo is built and then bounce requests to a Zuo script.
If you're curious about the details, see replacing the makefiles and other build scripts by mflatt · Pull Request #4179 · racket/racket · GitHub.
This change is not part of the upcoming v8.5 release. It will affect v8.6 and later.