MFC r271743:

  Implement most of timer_{create,settime,gettime,getoverrun,delete}
  for amd64/linux32.  Fix the entirely bogus (untested) version from
  r161310 for i386/linux using the same shared code in compat/linux.

  It is unclear to me if we could support more clock mappings but
  the current set allows me to successfully run commercial
  32bit linux software under linuxolator on amd64.

  Reviewed by:			jhb
  Differential Revision:	D784
Sponsored by:			DARPA, AFRL
Approved by:			re (gjb)
This is a direct commit rather than an MFC of r271744.

  Re-gen after r272020 (r271743 in head) implementing most of
  timer_{create,settime,gettime,getoverrun,delete}.

Approved by:	re (gjb)
Sponsored by:	DARPA/AFRL