lib/systems: add minimal s390x-linux cross-compile support

Tested basic functionality as:

    $ nix-build --arg crossSystem '{ config = "s390x-unknown-linux-gnu"; }' -A re2c
    $ file ./result/bin/re2c
    $ ./result/bin/re2c: ELF 64-bit MSB executable, IBM S/390, version 1 (SYSV),
    dynamically linked, interpreter ...-gnu-2.33-50/lib/ld64.so.1, for GNU/Linux 2.6.32, not stripped
    $ qemu-s390x ./result/bin/re2c --version
    re2c 2.2

lib/systems/default.nix

@@ -107,6 +107,7 @@ rec {
         else if final.isMips then "mips"
         else if final.isPower then "powerpc"
         else if final.isRiscV then "riscv"
+        else if final.isS390 then "s390"
         else final.parsed.cpu.name;
 
       qemuArch =

lib/systems/doubles.nix

@@ -28,7 +28,7 @@ let
     "aarch64-linux" "armv5tel-linux" "armv6l-linux" "armv7a-linux"
     "armv7l-linux" "i686-linux" "m68k-linux" "mipsel-linux"
     "powerpc64-linux" "powerpc64le-linux" "riscv32-linux"
-    "riscv64-linux" "s390-linux" "x86_64-linux"
+    "riscv64-linux" "s390-linux" "s390x-linux" "x86_64-linux"
 
     # MMIXware
     "mmix-mmixware"
@@ -41,7 +41,8 @@ let
     # none
     "aarch64-none" "arm-none" "armv6l-none" "avr-none" "i686-none"
     "msp430-none" "or1k-none" "m68k-none" "powerpc-none"
-    "riscv32-none" "riscv64-none" "s390-none" "vc4-none" "x86_64-none"
+    "riscv32-none" "riscv64-none" "s390-none" "s390x-none" "vc4-none"
+    "x86_64-none"
 
     # OpenBSD
     "i686-openbsd" "x86_64-openbsd"

lib/systems/examples.nix

@@ -152,6 +152,10 @@ rec {
     config = "s390-unknown-linux-gnu";
   };
 
+  s390x = {
+    config = "s390x-unknown-linux-gnu";
+  };
+
   arm-embedded = {
     config = "arm-none-eabi";
     libc = "newlib";

lib/systems/parse.nix

@@ -106,6 +106,7 @@ rec {
     riscv64  = { bits = 64; significantByte = littleEndian; family = "riscv"; };
 
     s390     = { bits = 32; significantByte = bigEndian; family = "s390"; };
+    s390x    = { bits = 64; significantByte = bigEndian; family = "s390"; };
 
     sparc    = { bits = 32; significantByte = bigEndian;    family = "sparc"; };
     sparc64  = { bits = 64; significantByte = bigEndian;    family = "sparc"; };

lib/tests/systems.nix

@@ -28,7 +28,7 @@ with lib.systems.doubles; lib.runTests {
   testredox = mseteq redox [ "x86_64-redox" ];
   testgnu = mseteq gnu (linux /* ++ kfreebsd ++ ... */);
   testillumos = mseteq illumos [ "x86_64-solaris" ];
-  testlinux = mseteq linux [ "aarch64-linux" "armv5tel-linux" "armv6l-linux" "armv7a-linux" "armv7l-linux" "i686-linux" "mipsel-linux" "riscv32-linux" "riscv64-linux" "x86_64-linux" "powerpc64-linux" "powerpc64le-linux" "m68k-linux" "s390-linux" ];
+  testlinux = mseteq linux [ "aarch64-linux" "armv5tel-linux" "armv6l-linux" "armv7a-linux" "armv7l-linux" "i686-linux" "mipsel-linux" "riscv32-linux" "riscv64-linux" "x86_64-linux" "powerpc64-linux" "powerpc64le-linux" "m68k-linux" "s390-linux" "s390x-linux" ];
   testnetbsd = mseteq netbsd [ "aarch64-netbsd" "armv6l-netbsd" "armv7a-netbsd" "armv7l-netbsd" "i686-netbsd" "m68k-netbsd" "mipsel-netbsd" "powerpc-netbsd" "riscv32-netbsd" "riscv64-netbsd" "x86_64-netbsd" ];
   testopenbsd = mseteq openbsd [ "i686-openbsd" "x86_64-openbsd" ];
   testwindows = mseteq windows [ "i686-cygwin" "x86_64-cygwin" "i686-windows" "x86_64-windows" ];