Merge pull request #37600 from abbradar/impureusenative

impureUseNativeOptimizations: add stdenv adapter

pkgs/stdenv/adapters.nix

@@ -171,4 +171,19 @@ rec {
         NIX_CFLAGS_LINK = toString (args.NIX_CFLAGS_LINK or "") + " -fuse-ld=gold";
       });
     };
+
+
+  /* Modify a stdenv so that it builds binaries optimized specifically
+     for the machine they are built on.
+
+     WARNING: this breaks purity! */
+  impureUseNativeOptimizations = stdenv: stdenv //
+    { mkDerivation = args: stdenv.mkDerivation (args // {
+        NIX_CFLAGS_COMPILE = toString (args.NIX_CFLAGS_COMPILE or "") + " -march=native";
+        NIX_ENFORCE_NO_NATIVE = false;
+
+        preferLocalBuild = true;
+        allowSubstitutes = false;
+      });
+    };
 }