Revert "gsl: update from 1.15 to 1.16"
Revert "gsl: update from 1.15 to 1.16"

Tests fail on i686: http://savannah.gnu.org/bugs/?40176

This reverts commit 6a69d7e89815599404a7c3f837327fd60da8b899.

NixOS/nixpkgs,SymbiFlow/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,SymbiFlow/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,triton/triton,triton/triton,SymbiFlow/nixpkgs,NixOS/nixpkgs,triton/triton,NixOS/nixpkgs,triton/triton,SymbiFlow/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,SymbiFlow/nixpkgs,triton/triton,triton/triton,triton/triton,triton/triton,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,SymbiFlow/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,SymbiFlow/nixpkgs,SymbiFlow/nixpkgs