qtspeech: fix build on Darwin

pkgs/development/libraries/qt-6/modules/qtspeech.nix

@@ -2,6 +2,7 @@
   qtModule,
   lib,
   stdenv,
+  llvmPackages,
   qtbase,
   qtmultimedia,
   pkg-config,
@@ -12,7 +13,10 @@
 
 qtModule {
   pname = "qtspeech";
-  nativeBuildInputs = [ pkg-config ];
+  nativeBuildInputs = [
+    pkg-config
+  ]
+  ++ lib.optionals stdenv.hostPlatform.isDarwin [ llvmPackages.lld ];
   buildInputs = lib.optionals stdenv.hostPlatform.isLinux [
     flite
     alsa-lib
@@ -22,4 +26,9 @@ qtModule {
     qtbase
     qtmultimedia
   ];
+  env = lib.optionalAttrs stdenv.hostPlatform.isDarwin {
+    # Work around ld64's libc++ hardening issue.
+    # TODO: Remove once #536365 reaches this branch.
+    NIX_CFLAGS_LINK = "-fuse-ld=lld";
+  };
 }