gdbsupport: move libxxhash configure check to gdbsupport

The following patch moves the fast_hash function, which uses libxxhash,
to gdbsupport.  Move the libxxhash configure check to gdbsupport (and
transitively to gdbserver).

Change-Id: I242499e50c8cd6fe9f51e6e92dc53a1b3daaa96e
Approved-By: Andrew Burgess <aburgess@redhat.com>
8 files changed