configd: fix build with clang 16

This is an additional fix for clang 16, which fails due to an undeclared
symbol. Adding `_DNS_SD_LIBDISPATCH` makes the symbol visible in
`dns_sd.h`, allowing the build to complete successfully.

pkgs/os-specific/darwin/apple-source-releases/configd/default.nix

@@ -13,6 +13,7 @@ appleDerivation' stdenv {
     NIX_CFLAGS_COMPILE = toString [
       "-ISystemConfiguration.framework/Headers"
       "-I${xnu}/Library/Frameworks/System.framework/Versions/B/PrivateHeaders"
+      "-D_DNS_SD_LIBDISPATCH" # Needed for DNSServiceSetDispatchQueue to be available
     ];
   };