xorg-server: disable false positive buffer overrun check

The bounds checks introduced by `-D_FORTIFY_SOURCE=2` in functions
like `strlcpy` interact poorly with data structures that treat fixed
sized arrays as flexible arrays (e.g. `struct sockaddr`).  This bug
manifested as an endless crashloop in XQuartz.

See also https://github.com/llvm/llvm-project/issues/29694

(cherry picked from commit 44f2933184)

pkgs/by-name/xo/xorg-server/package.nix

@@ -176,6 +176,9 @@ stdenv.mkDerivation (finalAttrs: {
       --subst-var-by XQUARTZ_APP "$out/Applications/XQuartz.app"
   '';
 
+  # avoid linux rebuilds
+  ${if stdenv.hostPlatform.isDarwin then "hardeningDisable" else null} = [ "strictflexarrays1" ];
+
   # default X install symlinks this to Xorg, we want XQuartz
   postInstall = lib.optionalString stdenv.hostPlatform.isDarwin ''
     ln -sf $out/bin/Xquartz $out/bin/X