mesa: fix build without valgrind

Since the update to mesa v23.1.1 the build without valgrind was broken.
This is a result of a change in mesa meson_options.txt which made the
valgrind support a feature in mesa:

https://gitlab.freedesktop.org/mesa/mesa/-/commit/3f10a89180b5638d2c1870e91e06aeae67925717#0cc1139e3347f573ae1feee5b73dbc8a8a21fcfa_1844_1829

So it must be explicitly turned off as it is now on by default.

pkgs/development/libraries/mesa/default.nix

@@ -210,6 +210,8 @@ self = stdenv.mkDerivation {
     # Rusticl, new OpenCL frontend
     "-Dgallium-rusticl=true" "-Drust_std=2021"
     "-Dclang-libdir=${llvmPackages.clang-unwrapped.lib}/lib"
+  ]  ++ lib.optionals (!withValgrind) [
+    "-Dvalgrind=disabled"
   ] ++ lib.optional enablePatentEncumberedCodecs
     "-Dvideo-codecs=h264dec,h264enc,h265dec,h265enc,vc1dec"
   ++ lib.optional (vulkanLayers != []) "-D vulkan-layers=${builtins.concatStringsSep "," vulkanLayers}";