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>

 --- trunk/src/acos.c	2009/12/08 16:49:43	733

 +++ trunk/src/acos.c	2009/12/09 20:51:38	734

 @@ -188,10 +188,7 @@

    else

      rnd_im = rnd_im == GMP_RNDU ? GMP_RNDD

        : rnd_im == GMP_RNDD ? GMP_RNDU

 -#if MPFR_VERSION_MAJOR >= 3

 -      : rnd_im == GMP_RNDA ? GMP_RNDZ

 -#endif

 -      : rnd_im;

 +      : rnd_im; /* both RNDZ and RNDA map to themselves for -asin(z) */

    rnd1 = RNDC(GMP_RNDN, rnd_im);

    mpfr_init2 (pi_over_2, p);

    for (;;)