Add simd module

lib/nix.nix

@@ -0,0 +1,8 @@
+{ lib, ... }:
+
+{
+  # taken from https://github.com/NixOS/nixpkgs/blob/master/nixos/modules/services/misc/nix-daemon.nix#L828-L832
+  # a builder can run code for `gcc.arch` and inferior architectures
+  gcc-system-features = arch: [ "gccarch-${arch}" ]
+    ++ map (x: "gccarch-${x}") lib.systems.architectures.inferiors.${arch};
+}

modules/simd.nix

@@ -0,0 +1,27 @@
+{ config, lib, libS, ... }:
+
+let
+  cfg = config.simd;
+in
+{
+  options.simd = {
+    enable = lib.mkEnableOption "optimized builds with simd instructions";
+    arch = lib.mkOption {
+      type = with lib.types; nullOr str;
+      default = null;
+      description = ''
+        Microarchitecture string for nixpkgs.hostPlatform.gcc.march and to generate system-features.
+        Can be determined with: ``gcc -march=native -Q --help=target | grep march``
+      '';
+    };
+  };
+
+  config = {
+    nix.settings.system-features = lib.mkIf (cfg.arch != null) (libS.nix.gcc-system-features config.simd.arch);
+
+    nixpkgs.hostPlatform = lib.mkIf cfg.enable {
+      gcc.arch = config.sandro.simd.arch;
+      inherit (config.nixpkgs) system;
+    };
+  };
+}