gemconfig: add eventmachine and msgpack

pkgs/development/interpreters/ruby/gemconfig/default.nix

···
 , libiconv, postgresql, v8_3_16_14, clang, sqlite, zlib, imagemagick
 , pkgconfig , ncurses, xapian, gpgme, utillinux, fetchpatch, tzdata, icu, libffi
 , cmake, libssh2, openssl, mysql, darwin, git, perl, gecode_3, curl
+, libmsgpack
 }:
 
 let
···
       installPath=$(cat $out/nix-support/gem-meta/install-path)
       sed -i $installPath/lib/dep-selector-libgecode.rb -e 's@VENDORED_GECODE_DIR =.*@VENDORED_GECODE_DIR = "${gecode_3}"@'
     '';
+  };
+
+  eventmachine = attrs: {
+    buildInputs = [ openssl ];
   };
 
   ffi = attrs: {
···
   libv8 = attrs: {
     buildInputs = [ which v8 python ];
     buildFlags = [ "--with-system-v8=true" ];
+  };
+
+  msgpack = attrs: {
+    buildInputs = [ libmsgpack ];
   };
 
   mysql2 = attrs: {