use @MAKEJOBS@ variable in simfactory machine ini files

[Roland Haas]

Simfactory has for some time supported a -j option that would let one change (or speficy eg on a freshly configured laptop) how many parallel processes to use when building. This functionality was reviewed and accepted in #1928 however to date no machine.ini file actually implements it so that user choices for -j are ignored.

Unless objected until 2019-04-14 I will go ahead and replace constructs like this:

make = make -j 17

by

makejobs = 17
make -j @MAKEJOBS@

which keeps the current default intact but lets the user change this via simfactory/bin/sim build -j 42 at build time (or in their defs.local.ini if they so choose).

To recap the discussion in #1928: if neither the machine database nor the user specifies a value for @MAKEJOBS@ then it defaults to 1 which is how make alone would behave.

As a side effect (and partial driver for this) this would mean that one can change the tutorial instructions from the odd

simfactory/bin/sim build --mdbentry make 'make -j2'

to

simfactory/bin/sim build --jobs 2

which seems easier on the eyes.

[Roland Haas]

Applied as git hash 6576596 "wheeler: use makejobs" of simfactory2.