[DRE-maint] Bug#774618: FTBFS on arm64, mips64el and ppc64el

[Edmund Grimley Evans]

> There are lots of warnings like this:
> > sspsv.c:67:5: warning: format '%d' expects argument of type 'int', but argument 3 has type 'integer'
>
> Which I'm guessing cause the buffer overflow when the tests are run:

I don't think those warnings cause the crash, though that should be
fixed, too, of course.

The cause of the crash is almost certainly this line, which appears
twice in ext/f2c_minimal.h
(https://sources.debian.net/src/ruby-lapack/1.7.1-1/ext/f2c_minimal.h/):

#if defined(__alpha__) || defined(__sparc64__) || defined(__x86_64__) || defined(__ia64__)

I think you could just add the failing 64-bit architectures to that
list: defined(__aarch64__) for arm64; see
https://wiki.debian.org/ArchitectureSpecificsMemo for the others.

(Note that this is, presumably, not supposed to be a list of all
"64-bit architectures". The package seems to be working on s390x and
ppc64, although they are "64-bit architectures" and not in the list. I
think the code here is mapping Fortran types to C types. Perhaps one
should get that information from libf2c2-dev, but that package is very
old and does not take account of arm64, so that approach wouldn't
currently work.)