Properly decode architecture type in GDBRemoteCommunicationClient::GetCurrentProcessInfo.

Instead of forcing the remote arch type to MachO all the time, we
inspect the OS/vendor that the remote debug server reports and use it to
set the arch type to MachO, ELF or COFF accordingly.

See thread here for more context:
http://lists.cs.uiuc.edu/pipermail/lldb-commits/Week-of-Mon-20140915/012968.html

Change by Stephane Sezer.

Tested:
MacOSX 10.9.4 x86_64
Ubuntu 14.04 x86_64