Merge lldb-platform and lldb-gdbserver into a single binary

This commit merges lldb-platform and lldb-gdbserver into a single binary
of the same size as each of the previous individual binaries. Execution
mode is controlled by the first argument being either platform or
gdbserver.

Patch from: flackr <flackr@google.com>

Differential revision: http://reviews.llvm.org/D7545

llvm-svn: 229683