pkgsStatic.valgrind: mark broken

Static-only Valgrind builds aren't supported, because it always tries
to build shared preload libraries. Marking it broken like this will
fix packages like pkgsStatic.libdrm that only use Valgrind if it's
available.

pkgs/development/tools/analysis/valgrind/default.nix

···
       "riscv32-linux" "riscv64-linux"
       "alpha-linux"
     ];
-    broken = stdenv.isDarwin; # https://hydra.nixos.org/build/128521440/nixlog/2
+    broken = stdenv.isDarwin || stdenv.hostPlatform.isStatic; # https://hydra.nixos.org/build/128521440/nixlog/2
   };
 }