btrfs-progs: fix static build (#425680)

pkgs/by-name/bt/btrfs-progs/package.nix

@@ -71,6 +71,10 @@ stdenv.mkDerivation rec {
   ]
   ++ lib.optionals (!udevSupport) [
     "--disable-libudev"
+  ]
+  ++ lib.optionals (stdenv.hostPlatform != stdenv.buildPlatform) [
+    "ac_cv_func_malloc_0_nonnull=yes"
+    "ac_cv_func_realloc_0_nonnull=yes"
   ];
 
   makeFlags = [ "udevruledir=$(out)/lib/udev/rules.d" ];