Fix the ability of "lldb-platform" to upload files.

The issue was GDBRemoteCommunication::CheckForPacket() already fixes up any prefixed bytes (0x7d followed by value that is XOR'ed with 0x20). If we do this again, we cause binary packets to lose bytes.

This allows lldb-platform to be able to upload binaries and debug them remotely.

llvm-svn: 218002