Hi,

the attached patch adds pypy3, a Python 3 JIT. As you can see this is a
lot of work, because pypy’s build system is rather unconventional.  I’m
not adding pypy2, because Python 2 is essentially EOL.

I’ve tried fixing as many testcases as possible, but there are some I
don’t know how to fix. Thus I’m disabling the test suite, although
everything is in place to run it. pypy itself works fine though, the
build is reproducible and passes `guix lint`.

One thing I don’t like right now is the dependency on gcc-toolchain
(i.e. gcc and binutils) in distutils. I don’t know how to avoid that,
since building CFFI modules won’t work without patching.

I guess the next step would be figuring out how to add “pypy3-foo”
variants for our Python packages, right?

Cheers,
Lars