[bug#55757] reproducible builds: disable parllel build in isl

[Vagrant Cascadian <vagrant@reproducible-builds.org>]

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The attached patch makes isl build reproducibly in guix by disabling
parallelism.

Admittedly, I'm unsure what the root cause is, and Debian's build of isl
does not appear to have this problem, despite building in parallel.

Seems like patches to isl should go to core-updates:

  $ guix refresh --list-dependent isl                                                               
  Building the following 2192 packages would ensure 5967 dependent packages are rebuilt: ...


live well,
  vagrant

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From 234e662df27771742b3e8b82e2115284e1cab5a8 Mon Sep 17 00:00:00 2001
From: Vagrant Cascadian <vagrant@reproducible-builds.org>
Date: Wed, 1 Jun 2022 11:58:41 -0700
Subject: [PATCH 1/4] gnu: isl: Disable parallel build.

* gnu/packages/gcc.scm (isl)[arguments]: Pass parallel-build #f.
---
 gnu/packages/gcc.scm | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/gnu/packages/gcc.scm b/gnu/packages/gcc.scm
index cd144772b8..560a35af2d 100644
--- a/gnu/packages/gcc.scm
+++ b/gnu/packages/gcc.scm
@@ -1218,7 +1218,8 @@ (define-public isl
     (build-system gnu-build-system)
     (outputs '("out" "static"))
     (arguments
-     '(#:phases (modify-phases %standard-phases
+     '(#:parallel-build? #f
+       #:phases (modify-phases %standard-phases
                   (add-after 'install 'move-static-library
                     (lambda* (#:key outputs #:allow-other-keys)
                       (let* ((out (assoc-ref outputs "out"))
-- 
2.35.1


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