Hack flake to ensure x86-64-v3

The important bit is it -v3, it ensures AVX levels supported by
customers' machines.

Author: blackheaven

flake.nix

@@ -99,6 +99,10 @@
             (import ./nix/overlay.nix)
             (import ./nix/overlay-docs.nix)
           ];
+          # Target x86-64-v3 microarchitecture only on x86_64 systems
+          config = nixpkgs.lib.optionalAttrs (nixpkgs.lib.hasPrefix "x86_64-" system) {
+            replaceStdenv = { pkgs }: pkgs.stdenvAdapters.withCFlags [ "-march=x86-64-v3" ] pkgs.stdenv;
+          };
         };
         pkgs_24_11 = import nixpkgs_24_11 {
           inherit system;