Fixes <https://bugs.gnu.org/43668>.
Previously, guix-daemon would try to run GNU/Hurd executables on
GNU/Linux. execve(2) would succeed, but the executable would
immediately crash.
This change prevents it from attempting to execute "i586-gnu" code on
"*-linux", while preserving the binfmt_misc-friendly behavior
implemented in commit 7bf2a70a4ffd976d50638d3b9f2ec409763157df.
* nix/libstore/build.cc (sameOperatingSystemKernel): New function.
(DerivationGoal::runChild): Call 'execve' only when
'sameOperatingSystemKernel' returns true.
9556ac498f