FIx XCode project files for lldb

Summary:
Fixes the XCode builds that started failing when i added CompletionRequest.cpp/.h.

The patch is so large because XCode decided to write the lines back in its own order, but essentially we only added on e file.

Subscribers: srhines, lldb-commits

Differential Revision: https://reviews.llvm.org/D48858

llvm-svn: 336154