bug#21803: Guitarix builds non-deterministically

[Ludovic Courtès]

Guitarix 0.33.0, as of Guix commit 3c3e697, builds
non-deterministically:

--8<---------------cut here---------------start------------->8---
$ ./pre-inst-env guix challenge guitarix
updating list of substitutes from 'http://hydra.gnu.org'... 100.0%
/gnu/store/6ksnwcqn92z2nf6qw5js7njnfqlifgpb-guitarix-0.33.0 contents differ:
  local hash: 1rh7qxmylsbsaah59h7sclqqxcz0lwsixlc0krkzwhx8gfhlyam6
  http://hydra.gnu.org/nar/6ksnwcqn92z2nf6qw5js7njnfqlifgpb-guitarix-0.33.0: 
1cq4k1wdqibwraqk0wkjj6n5hgs9v9zcvwr2wfgxvgxnf5l1rfhf
$ wget -q -O - 
http://hydra.gnu.org/nar/6ksnwcqn92z2nf6qw5js7njnfqlifgpb-guitarix-0.33.0 | 
bunzip2 | guix archive -x t
$ LC_ALL=C diff -r /gnu/store/6ksnwcqn92z2nf6qw5js7njnfqlifgpb-guitarix-0.33.0 t
$ LC_ALL=C diff -r --no-dereference 
/gnu/store/6ksnwcqn92z2nf6qw5js7njnfqlifgpb-guitarix-0.33.0 t
File /gnu/store/6ksnwcqn92z2nf6qw5js7njnfqlifgpb-guitarix-0.33.0/lib/libgxw.so 
is a symbolic link while file t/lib/libgxw.so is a regular file
--8<---------------cut here---------------end--------------->8---

It appears to create libgxw.so either as a symlink or as a regular file
in a non-deterministic fashion.

It would be nice to see why this happens, and whether this affects all
Waf-based packages.

Ludo’.