feat: Bundle debug symbols in "mcrouter-debug" package

[dalehamel]

We have encountered a mcrouter segmentation fault in production, but the thread trace from lldb is not very helpful:

(lldb) bt all
* thread #1, name = 'mcrouter', stop reason = signal SIGSEGV
  * frame #0: 0x000055b8c46881f8 mcrouter`___lldb_unnamed_symbol696$$mcrouter + 8
  thread #2, stop reason = signal 0
    frame #0: 0x00007f43885c5d2d
  thread #3, stop reason = signal 0
    frame #0: 0x00007f43877a7bb7
  thread #4, stop reason = signal 0
    frame #0: 0x00007f43885caf85
  thread #5, stop reason = signal 0
    frame #0: 0x00007f43885caf85

As an aside, it is also bizarre that only one frame is shown for each thread, but perhaps this is also due to the lack of symbols (I am not especially well acquainted with lldb, and I'm not sure if it needs symbols to be able to walk the stack from a coredump, in my experience it is usually not a problem in gdb at least).

There doesn't seem to be any separate mcrouter-debug package available, and I can't determine where in the build process the mcrouter binary is stripped.

I'd like to suggest / request that the build process retain the output of stripping the release binary, and use this to produce a mcrouter-debug package which can be installed for analyzing crashes and debugging mcrouter.