Merge pull request #12920 from NixOS/mergify/bp/2.27-maintenance/pr-12919

Reinstate Darwin minversion (backport #12919)

flake.nix

@@ -177,7 +177,7 @@
               {
                 otherSplices = final.generateSplicesForMkScope "nixDependencies";
                 f = import ./packaging/dependencies.nix {
-                  inherit stdenv;
+                  inherit inputs stdenv;
                   pkgs = final;
                 };
               };

packaging/dependencies.nix

@@ -1,14 +1,36 @@
 # These overrides are applied to the dependencies of the Nix components.
 
 {
+  # Flake inputs; used for sources
+  inputs,
+
   # The raw Nixpkgs, not affected by this scope
   pkgs,
 
   stdenv,
 }:
 
+let
+  prevStdenv = stdenv;
+in
+
 let
   inherit (pkgs) lib;
+
+  stdenv = if prevStdenv.isDarwin && prevStdenv.isx86_64 then darwinStdenv else prevStdenv;
+
+  # Fix the following error with the default x86_64-darwin SDK:
+  #
+  #     error: aligned allocation function of type 'void *(std::size_t, std::align_val_t)' is only available on macOS 10.13 or newer
+  #
+  # Despite the use of the 10.13 deployment target here, the aligned
+  # allocation function Clang uses with this setting actually works
+  # all the way back to 10.6.
+  # NOTE: this is not just a version constraint, but a request to make Darwin
+  #       provide this version level of support. Removing this minimum version
+  #       request will regress the above error.
+  darwinStdenv = pkgs.overrideSDK prevStdenv { darwinMinVersion = "10.13"; };
+
 in
 scope: {
   inherit stdenv;