Fix llgs to send triple for non-Apple platforms and lldb to interpret correctly.

This change addresses this bug:
http://llvm.org/bugs/show_bug.cgi?id=20755

This change:
* Modifies llgs to send triple instead of cputype and cpusubtype when not on Apple platforms in qProcessInfo.
* Modifies lldb's GDBRemoteCommunicationClient to handle the triple returned from qProcessInfo if given.
  When given, it will prefer to use triple over cputype and cpusubtype.
* Adds gdb-remote protocol tests to verify that cputype and cpusubtype are specified on darwin, and that triple is specified on Linux.

llvm-svn: 216470