qt5{12,14,15}: use default stdenv on darwin

pkgs/development/libraries/qt-5/5.12/default.nix

@@ -18,7 +18,7 @@ top-level attribute to `top-level/all-packages.nix`.
 , lib, stdenv, fetchurl, fetchpatch, fetchFromGitHub, makeSetupHook, makeWrapper
 , bison, cups ? null, harfbuzz, libGL, perl
 , gstreamer, gst-plugins-base, gtk3, dconf
-, llvmPackages_5, darwin
+, darwin
 
   # options
 , developerBuild ? false
@@ -30,8 +30,6 @@ let
 
   qtCompatVersion = srcs.qtbase.version;
 
-  stdenvActual = if stdenv.cc.isClang then llvmPackages_5.stdenv else stdenv;
-
   mirror = "https://download.qt.io";
   srcs = import ./srcs.nix { inherit fetchurl; inherit mirror; } // {
     # Community port of the now unmaintained upstream qtwebkit.
@@ -129,7 +127,7 @@ let
       mkDerivation =
         import ../mkDerivation.nix
         { inherit lib; inherit debug; wrapQtAppsHook = null; }
-        stdenvActual.mkDerivation;
+        stdenv.mkDerivation;
     }
     { inherit self srcs patches; };
 
@@ -144,7 +142,7 @@ let
         import ../mkDerivation.nix
         { inherit lib; inherit debug; inherit (self) wrapQtAppsHook; };
 
-      mkDerivation = mkDerivationWith stdenvActual.mkDerivation;
+      mkDerivation = mkDerivationWith stdenv.mkDerivation;
 
       qtbase = callPackage ../modules/qtbase.nix {
         inherit (srcs.qtbase) src version;
@@ -193,7 +191,6 @@ let
         inherit (darwin.apple_sdk.libs) sandbox;
         inherit (darwin.apple_sdk.frameworks) ApplicationServices AVFoundation Foundation ForceFeedback GameController AppKit
           ImageCaptureCore CoreBluetooth IOBluetooth CoreWLAN Quartz Cocoa LocalAuthentication;
-        stdenv = stdenvActual;
       };
       qtwebglplugin = callPackage ../modules/qtwebglplugin.nix {};
       qtwebkit = callPackage ../modules/qtwebkit.nix {

pkgs/development/libraries/qt-5/5.14/default.nix

@@ -18,7 +18,7 @@ top-level attribute to `top-level/all-packages.nix`.
 , lib, stdenv, fetchurl, fetchpatch, fetchFromGitHub, makeSetupHook, makeWrapper
 , bison, cups ? null, harfbuzz, libGL, perl
 , gstreamer, gst-plugins-base, gtk3, dconf
-, llvmPackages_5, darwin
+, darwin
 
   # options
 , developerBuild ? false
@@ -30,8 +30,6 @@ let
 
   qtCompatVersion = srcs.qtbase.version;
 
-  stdenvActual = if stdenv.cc.isClang then llvmPackages_5.stdenv else stdenv;
-
   mirror = "https://download.qt.io";
   srcs = import ./srcs.nix { inherit fetchurl; inherit mirror; } // {
     # qtwebkit does not have an official release tarball on the qt mirror and is
@@ -130,7 +128,7 @@ let
       mkDerivation =
         import ../mkDerivation.nix
         { inherit lib; inherit debug; wrapQtAppsHook = null; }
-        stdenvActual.mkDerivation;
+        stdenv.mkDerivation;
     }
     { inherit self srcs patches; };
 
@@ -145,7 +143,7 @@ let
         import ../mkDerivation.nix
         { inherit lib; inherit debug; inherit (self) wrapQtAppsHook; };
 
-      mkDerivation = mkDerivationWith stdenvActual.mkDerivation;
+      mkDerivation = mkDerivationWith stdenv.mkDerivation;
 
       qtbase = callPackage ../modules/qtbase.nix {
         inherit (srcs.qtbase) src version;

pkgs/development/libraries/qt-5/5.15/default.nix

@@ -11,7 +11,7 @@ Check for any minor version changes.
 , lib, stdenv, fetchurl, fetchgit, fetchpatch, fetchFromGitHub, makeSetupHook, makeWrapper
 , bison, cups ? null, harfbuzz, libGL, perl
 , gstreamer, gst-plugins-base, gtk3, dconf
-, llvmPackages_5, darwin
+, darwin
 
   # options
 , developerBuild ? false
@@ -25,8 +25,6 @@ let
 
   qtCompatVersion = srcs.qtbase.version;
 
-  stdenvActual = if stdenv.cc.isClang then llvmPackages_5.stdenv else stdenv;
-
   patches = {
     qtbase = lib.optionals stdenv.isDarwin [
       ./qtbase.patch.d/0001-qtbase-mkspecs-mac.patch
@@ -92,7 +90,7 @@ let
       mkDerivation =
         import ../mkDerivation.nix
         { inherit lib; inherit debug; wrapQtAppsHook = null; }
-        stdenvActual.mkDerivation;
+        stdenv.mkDerivation;
     }
     { inherit self srcs patches; };
 
@@ -107,7 +105,7 @@ let
         import ../mkDerivation.nix
         { inherit lib; inherit debug; inherit (self) wrapQtAppsHook; };
 
-      mkDerivation = mkDerivationWith stdenvActual.mkDerivation;
+      mkDerivation = mkDerivationWith stdenv.mkDerivation;
 
       qtbase = callPackage ../modules/qtbase.nix {
         inherit (srcs.qtbase) src version;

pkgs/top-level/all-packages.nix

@@ -19436,7 +19436,7 @@ with pkgs;
       inherit lib stdenv fetchurl fetchpatch fetchFromGitHub makeSetupHook makeWrapper;
       inherit bison cups dconf harfbuzz libGL perl gtk3;
       inherit (gst_all_1) gstreamer gst-plugins-base;
-      inherit llvmPackages_5 darwin;
+      inherit darwin;
     });
 
   qt514 = recurseIntoAttrs (makeOverridable
@@ -19445,7 +19445,7 @@ with pkgs;
       inherit lib stdenv fetchurl fetchpatch fetchFromGitHub makeSetupHook makeWrapper;
       inherit bison cups dconf harfbuzz libGL perl gtk3;
       inherit (gst_all_1) gstreamer gst-plugins-base;
-      inherit llvmPackages_5 darwin;
+      inherit darwin;
     });
 
   qt515 = recurseIntoAttrs (makeOverridable
@@ -19454,7 +19454,7 @@ with pkgs;
       inherit lib stdenv fetchurl fetchpatch fetchgit fetchFromGitHub makeSetupHook makeWrapper;
       inherit bison cups dconf harfbuzz libGL perl gtk3;
       inherit (gst_all_1) gstreamer gst-plugins-base;
-      inherit llvmPackages_5 darwin;
+      inherit darwin;
     });
 
   libsForQt512 = recurseIntoAttrs (import ./qt5-packages.nix {