static: set default_library flag for meson in makeStaticLibrary

Adds support for building static libraries with meson.

pkgs/stdenv/adapters.nix

@@ -60,6 +60,7 @@ rec {
           "--enable-static"
           "--disable-shared"
         ];
+        mesonFlags = (args.mesonFlags or []) ++ [ "-Ddefault_library=static" ];
       });
     };