With certain operating systems, certain compilers and certain compiler flags (in particular Cygwin with SAGE_DEBUG=yes), the PARI function is_universal_constant() can be broken. This leads to a 0 return value for closures returning gnil:

sage: pari("x -> print(x);")("hello")
hello
0

Upstream report: http://pari.math.u-bordeaux.fr/archives/pari-dev-1610/msg00006.html

This branch simply adds a patch from upstream.

Depends on #21582

Upstream: Fixed upstream, but not in a stable release.

Component: packages: standard

Keywords: pari windows cygwin

Author: Jeroen Demeyer

Branch: 0e7d231

Reviewer: Erik Bray

Issue created by migration from https://trac.sagemath.org/ticket/21637