Urs Liska provides installers for branch master of lilypond, generated by an updated version of our build system GUB:
https://cloud.ursliska.de/s/QPINwLqJNeVslCu
There you'll find
lilypond-2.21.0-1.darwin-ppc.tar.bz2
lilypond-2.21.0-1.darwin-x86.tar.bz2
lilypond-2.21.0-1.freebsd-64.sh
lilypond-2.21.0-1.freebsd-x86.sh
lilypond-2.21.0-1.linux-64.sh
lilypond-2.21.0-1.linux-ppc.sh
lilypond-2.21.0-1.linux-x86.sh
lilypond-2.21.0-1.mingw.exe
lilypond-2.21.0.tar.gz
Please test if those files provide valid lilypond installations and report success / failure by replying to this thread if no identical test results already have been posted.
The mingw.exe download appears to work fine in Frescobaldi running under Windows 10 Home on Intel Core i7-7500U cpu. I'll continue to use it for all future typesetting.