grub2: fix build w/ glibc-2.44

Co-authored-by: Philip Taron <philip.taron@gmail.com>

pkgs/by-name/gr/grub2/package.nix

@@ -223,6 +223,9 @@ stdenv.mkDerivation rec {
 
   strictDeps = true;
 
+  # glibc 2.43 C23 const-preserving strchr/strstr macros
+  env.NIX_CFLAGS_COMPILE = "-Wno-error=discarded-qualifiers";
+
   hardeningDisable = [ "all" ];
 
   separateDebugInfo = !xenSupport;