check: fix compilation on cross-compiled musl (#260675)

on cross-compiled musl vsnprintf gets detected as non-compliant with c99.
The included replacement is incompatible with SOURCE_FORTIFY.

pkgs/development/libraries/check/default.nix

···
     sha256 = "02m25y9m46pb6n46s51av62kpd936lkfv3b13kfpckgvmh5lxpm8";
   };
 
+  # fortify breaks the libcompat vsnprintf implementation
+  hardeningDisable = lib.optionals (stdenv.hostPlatform.isMusl && (stdenv.hostPlatform != stdenv.buildPlatform)) [ "fortify" ];
+
   # Test can randomly fail: https://hydra.nixos.org/build/7243912
   doCheck = false;