We should try to fix these warnings:

warning: -jN forced in submake: disabling jobserver mode.

There are 3 different issues:

1. The warnings appears several times at the top-level (not inside a package build) and during the build of the Sage library. This can probably be fixed by moving this snippet from sage-env higher up:

# If MAKEFLAGS exists, assume it got set by make.
# Therefore, remove all flags from $MAKE
if [ "${MAKEFLAGS-__unset__}" != "__unset__" ]; then
    MAKE=`echo "$MAKE" | sed 's/ .*//'`
fi
export MAKE

2. For several packages, the warning correctly appears because we explicitly force -j1 (presumably to fix parallel build issues):

• brial
• gap
• pari
• pkgconf
• python2
• singular
• zeromq

3. Other packages where this warnings appears:

• openblas: no idea where it comes from, probably the openblas build system itself.

CC: @embray @jdemeyer @vbraun @jhpalmieri @dimpase @orlitzky

Component: build

Issue created by migration from https://trac.sagemath.org/ticket/21610