More scrutable bootstrapping process

[Mario Domenech Goulart]

We currently have two ways to build CHICKEN:

• from release tarballs. In that case we have the C code generated by CHICKEN. In this case, the only requirement to build CHICKEN is a supported C toolchain and GNU Make. The C code in release tarballs is not really "source" code, as it can be considered inscrutable by most humans.

• from git. In this case we require a functional CHICKEN installation (i.e., binary format, compiled out of a release tarball -- see previous item) to compile Scheme code to C.

Currently the most scrutable way to build CHICKEN is using the C
code generated by CHICKEN to build CHICKEN. But then, as
previously mentioned, we assume the C code we are compiling is
thrustworthy, which can hardly be assessed as the C code is the
output of a compiler, so very hard to follow.

This ticket is about improving this situation, so that we can build
CHICKEN from git in a way that the whole process is more scrutable.

References:

• ​http://issues.guix.gnu.org/22366 points out the issue reported in this ticket.

• ​https://bootstrappable.org/ has more information on the benefits of transparent bootstrapping processes.