textproc/cast2gif: Fix for 32bit archs

Patch for internal cargo-crates/font-kit [1] to make
textproc/cast2gif also executable on 32bit platforms.

[1] https://github.com/servo/font-kit/commit/cc92c3fb65792fa716728407f5651343e1bbe155

PR: 251672
Submitted by: Nuno Teixeira <ed.arrakis@gmail.com> (maintainer)
Approved by: arrowd (mentor)
Differential Revision: https://reviews.freebsd.org/D27516