qt5.qtwebengine: use the 13.3 SDK because the 14.4 SDK does not work

While the 14.4 SDK works to build the rest of Qt 5, building Qt
WebEngine fails with errors like the following:

    In file included from gen/base/base_jumbo_37.cc:14:
    In file included from ./../../3rdparty/chromium/base/mac/mach_port_rendezvous.cc:16:
    In file included from ../../3rdparty/chromium/base/mac/foundation_util.h:34:
    In file included from /nix/store/sfdyfscmykycv7nfscn551lyl3gf4n27-apple-sdk-14.4/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/System/Library/Frameworks/ApplicationServices.framework/Headers/ApplicationServices.h:39:
    In file included from /nix/store/sfdyfscmykycv7nfscn551lyl3gf4n27-apple-sdk-14.4/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/System/Library/Frameworks/CoreText.framework/Headers/CoreText.h:26:
    In file included from /nix/store/sfdyfscmykycv7nfscn551lyl3gf4n27-apple-sdk-14.4/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/System/Library/Frameworks/CoreText.framework/Headers/CTFramesetter.h:21:
    In file included from /nix/store/sfdyfscmykycv7nfscn551lyl3gf4n27-apple-sdk-14.4/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/System/Library/Frameworks/CoreText.framework/Headers/CTTypesetter.h:20:
    /nix/store/sfdyfscmykycv7nfscn551lyl3gf4n27-apple-sdk-14.4/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/System/Library/Frameworks/CoreText.framework/Headers/CTLine.h:138:5: error: unknown type name 'CFAttributedStringRef'; did you mean 'CFMutableStringRef'?
        CFAttributedStringRef attrString ) CT_AVAILABLE(macos(10.5), ios(3.2), watchos(2.0), tvos(9.0));
        ^
    /nix/store/sfdyfscmykycv7nfscn551lyl3gf4n27-apple-sdk-14.4/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/System/Library/Frameworks/CoreFoundation.framework/Headers/CFBase.h:500:70: note: 'CFMutableStringRef' declared here
    typedef struct CF_BRIDGED_MUTABLE_TYPE(NSMutableString) __CFString * CFMutableStringRef;
                                                                     ^

pkgs/development/libraries/qt-5/modules/qtwebengine.nix

@@ -20,7 +20,7 @@
 , systemd
 , enableProprietaryCodecs ? true
 , gn
-, cctools, cups, bootstrap_cmds, xcbuild, writeScriptBin
+, apple-sdk_13, cctools, cups, bootstrap_cmds, xcbuild, writeScriptBin
 , ffmpeg ? null
 , lib, stdenv
 , version ? null
@@ -51,7 +51,8 @@ let
 
 in
 
-qtModule ({
+# Override the SDK because Qt WebEngine doesn’t seem to build using the 14.4 SDK.
+(qtModule.override { apple-sdk_for_qt = apple-sdk_13; }) ({
   pname = "qtwebengine";
   nativeBuildInputs = [
     bison flex git gperf ninja pkg-config (python.withPackages(ps: [ ps.html5lib ])) which gn nodejs

pkgs/development/libraries/qt-5/qtModule.nix

@@ -3,6 +3,7 @@
 , buildPackages
 , mkDerivation
 , apple-sdk_14
+, apple-sdk_for_qt ? apple-sdk_14
 , perl
 , qmake
 , patches
@@ -27,7 +28,7 @@ mkDerivation (args // {
   buildInputs =
     args.buildInputs or [ ]
     # Per https://doc.qt.io/qt-5/macos.html#supported-versions
-    ++ lib.optionals stdenv.isDarwin [ apple-sdk_14 ];
+    ++ lib.optionals stdenv.isDarwin [ apple-sdk_for_qt ];
 
   nativeBuildInputs =
     (args.nativeBuildInputs or []) ++ [