lib.systems, test.cross.sanity: add test case for #264989

We have several cross-compilation bugs that show up if
hostPlatform!=buildPlatform yet
hostPlatform.config==buildPlatform.config.

These bugs have appeared and disappeared as we've fiddled with the
definition of equality for platform objects. This commit adds a
clear-cut case where they are *not* equal and never will be, so we
can test it.

Changed files
+2
lib
systems
pkgs
test
cross
+1
lib/systems/examples.nix
···
};
gnu64 = { config = "x86_64-unknown-linux-gnu"; };
+
gnu64_simplekernel = gnu64 // platforms.pc_simplekernel; # see test/cross/default.nix
gnu32 = { config = "i686-unknown-linux-gnu"; };
musl64 = { config = "x86_64-unknown-linux-musl"; };
+1
pkgs/test/cross/default.nix
···
pkgs.pkgsMusl.stdenv
pkgs.pkgsLLVM.stdenv
pkgs.pkgsStatic.bash
+
#pkgs.pkgsCross.gnu64_simplekernel.bash # https://github.com/NixOS/nixpkgs/issues/264989
pkgs.pkgsCross.arm-embedded.stdenv
pkgs.pkgsCross.sheevaplug.stdenv # for armv5tel
pkgs.pkgsCross.raspberryPi.stdenv # for armv6l