comptools: add make-3.81

Since the advent of make-3.82, some packages now break due to changes
in make-3.82, being stricter than 3.81 when interpreting the Makefiles.

This has bugged us a bit too much so far, and I believe fixing all
of them is a long road, while simply building make-3.81 is the easiest
route for now.

Of course, in the long term, packages will get fixed upstream, and we
should back-port the fixes to old versions, and get rid of building
make-3.81. In the meantime...

Reported several times on the mailing list.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

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