(from jhpalmieri, #30123)

Note that sage -b doesn't work any more: it tries to do cd "$SAGE_SRC" && $MAKE, but SAGE_SRC/Makefile.in was removed in #29411. (If you have done an incremental build, the Makefile is still there.)

Depends on #30128

CC: @jhpalmieri @orlitzky @kliem

Component: build

Author: Matthias Koeppe, John Palmieri, Michael Orlitzky

Branch: 2d95def

Reviewer: John Palmieri, Matthias Koeppe

Issue created by migration from https://trac.sagemath.org/ticket/30153