ycmd: 2017-02-03 -> 2017-03-27

Now works with newer version of vim youcompleteme plugin.

Details:
- The OS X patch is no longer necessary as that code was removed upstream.
- It seems to want LLVM version 4 now.
- It annoyingly wants to symlink libclang.4 to libclang.4.0; nix already
  did this.