How many processes the link time work is spread over, which is what -flto= takes.
Named for the flag rather than for what it counts, because Jobs in the driver is already the
answer to how many files are compiled at once and the two numbers are not the same number.
The link time half of link time optimization is where all of the time goes, because it is the
half that has the whole program in front of it, and gcc’s answer is to cut the program into
pieces and generate code for the pieces at once. This says how many at once.
-flto=jobserver. As many as make is willing to hand out, asked for through the
jobserver pipe it puts in the environment, which is the only answer that does not fight
with the rest of a parallel build for the same cores.