bug#36811: Guix fails to build with libgc 8.0.4

Hi Jonathan,

As discussed yesterday on #guix, I tried this:

  guix build guile3.0-guix --with-input=libgc@7=libgc@8

as of Guix commit 9d0dfd9a9a7c43363a4e140c20d49f119fe6f2e3.  Guile 3.0.0
itself builds fine (test suite included), but the build of Guix crashes
like this (on x86_64-linux-gnu):

--8<---------------cut here---------------start------------->8---
[ 76%] GUILEC   gnu/packages/icu4c.go
[ 77%] GUILEC   gnu/packages/idris.go
[ 77%] GUILEC   gnu/packages/idutils.go
[ 77%] GUILEC   gnu/packages/image.go
[ 77%] GUILEC   gnu/packages/image-processing.go
[ 77%] GUILEC   gnu/packages/image-viewers.go
mmap(PROT_NONE) failed
/gnu/store/29jhbbg1hf557x8j53f9sxd9imlmf02a-bash-minimal-5.0.7/bin/bash: line 7: 26886 Aborted                 XDG_CACH
E_HOME=/nowhere host=x86_64-unknown-linux-gnu srcdir="." ./pre-inst-env /gnu/store/dcsjagbjlhjj40g30lb88wx3zybmh07g-gui
le-next-3.0.0/bin/guile -L "." -L "." --no-auto-compile -s "."/build-aux/compile-all.scm guix/base16.scm guix/base32.sc
m guix/base64.scm guix/ci.scm guix/cpio.scm guix/deprecation.scm guix/docker.scm guix/json.scm guix/records.scm guix/pk
--8<---------------cut here---------------end--------------->8---

Apparently the message and abort come from ‘GC_unmap’ or ‘GC_unmap_gap’
in libgc, but I have no idea what to think about it.  Could it be a heap
exhaustion issue or similar?  That’s not impossible.

Thanks,
Ludo’.