DynamicLoaderPOSIXDYLD now gets gdb-remote auxv data where appropriate.

The Process base class now has a virtual GetAuxvData() method, defaulting
to returning a null DataBufferSP.

ProcessGDBRemote defaults to asking the gdb-remote connection for the auxv
data.  ProcessPOSIX grab it from the Host::GetAuxvData() if the target platform
is the host; otherwise, it returns nothing (and shouldn't really get there AFAICT,
added assert).

ProcessElfCore.h continues to provide the data from the core file.

This is the key: AuxVector, used by DynamicLoaderPOSIXDYLD to load the auxv
data, now always asks the process for the auxv data.  That allows the
changes above to get ProcessGDBRemote gdb-remote protocol requests for
llgs connections, and to use the host system for local debugging.