luarocks: use targetPlatform.darwinMinVersion as default

pkgs/development/tools/misc/luarocks/darwin-3.1.3.patch

@@ -7,7 +7,7 @@ index c5af5a2..1949fdc 100644
        defaults.arch = "macosx-"..target_cpu
        defaults.variables.LIBFLAG = "-bundle -undefined dynamic_lookup -all_load"
 -      local version = util.popen_read("sw_vers -productVersion")
-+      local version = os.getenv("MACOSX_DEPLOYMENT_TARGET") or "10.12"
++      local version = os.getenv("MACOSX_DEPLOYMENT_TARGET") or "@darwinMinVersion@"
        version = tonumber(version and version:match("^[^.]+%.([^.]+)")) or 3
        if version >= 10 then
           version = 8

pkgs/development/tools/misc/luarocks/default.nix

@@ -19,6 +19,11 @@ stdenv.mkDerivation rec {
   };
 
   patches = [ ./darwin-3.1.3.patch ];
+
+  postPatch = lib.optionalString stdenv.targetPlatform.isDarwin ''
+    substituteInPlace src/luarocks/core/cfg.lua --subst-var-by 'darwinMinVersion' '${stdenv.targetPlatform.darwinMinVersion}'
+  '';
+
   preConfigure = ''
     lua -e "" || {
         luajit -e "" && {