HPCC-12094 Check if existing daserver running and abort out.

Existing mechanism was already in place for Windows builds using
a named mutex.
And there was already a named mutex implemented under Linux.

Signed-off-by: Jake Smith <jake.smith@lexisnexis.com>
Merge pull request #6353 from jakesmith/hpcc-12094

HPCC-12094 Check if existing daserver running and abort out.

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>