bug#52311: Flex and Bison are not built from source

[Ludovic Courtès]

Hello Guix!

As stikonas (Andrius Štikonas) rightfully pointed out on #guix, Flex and
Bison are currently not entirely built from source in Guix: their source
tarballs contain Flex- and/or Bison-generated files.

The problem and a solution are described here:

  https://gitlab.com/giomasce/nbs/

The “live-bootstrap” project also implements a multi-stage bootstrap:

  
https://github.com/fosslinux/live-bootstrap/blob/master/sysa/heirloom-devtools-070527/heirloom-devtools-070527.kaem
  
https://github.com/fosslinux/live-bootstrap/blob/master/sysa/flex-2.5.11/flex-2.5.11.sh
  
https://github.com/fosslinux/live-bootstrap/blob/master/sysa/flex-2.6.4/flex-2.6.4.sh
  https://github.com/fosslinux/live-bootstrap/tree/master/sysa/bison-3.4.1

Let’s follow their lead on the next core-updates cycle.

Thanks stikonas for the links!

Ludo’.