On aix (actually possible on any system) getloadavg fails and keeps errno intact.
This results in a bogus error message from make.
The patch resets errno before calling getloadavg.

$ cat makefile
MAKEFLAGS:=-Rr
all: 1.x 2.x 3.x 4.x

%.x:; sleep 10
makefile::;
$ ~/src/gmake/make-4.3.90/i64/make -j -l0.2
sleep 10
make: cannot enforce load limit: getloadavg: A file or directory in the path name does not exist.
sleep 10
sleep 10
sleep 10
$
$

# with this patch
$ ~/src/gmake/make-4.3.90/i64/make -j -l0.2
sleep 10
make: cannot enforce load limits on this operating system
sleep 10
sleep 10
sleep 10
$