Thanks for the patch! I rebuilt the musl libc, copied the lib to my old linux box and Postgres is running well now.
It's interesting that when I built Postgres on this same old Linux using the native libc but it fails to run.
============== removing existing temp installation ==============
============== creating temporary installation ==============
============== initializing database system ==============
============== starting postmaster ==============
pg_regress: postmaster did not respond within 60 seconds
Building with musl on a modern Linux works on an old Linux. But building Postgres on the old Linux with the native libc gives me a broken Postgres. That's why I'm interested in musl libc.