lib.systems: don't try to emulate s390-linux

We don't have an emulator that can do this.

lib/systems/default.nix

@@ -140,6 +140,7 @@ rec {
 
       qemuArch =
         if final.isAarch32 then "arm"
+        else if final.isS390 && !final.isS390x then null
         else if final.isx86_64 then "x86_64"
         else if final.isx86 then "i386"
         else final.uname.processor;
@@ -193,7 +194,7 @@ rec {
           then "${pkgs.runtimeShell} -c '\"$@\"' --"
           else if final.isWindows
           then "${wine}/bin/wine${lib.optionalString (final.parsed.cpu.bits == 64) "64"}"
-          else if final.isLinux && pkgs.stdenv.hostPlatform.isLinux
+          else if final.isLinux && pkgs.stdenv.hostPlatform.isLinux && final.qemuArch != null
           then "${qemu-user}/bin/qemu-${final.qemuArch}"
           else if final.isWasi
           then "${pkgs.wasmtime}/bin/wasmtime"