8164900: Add support for O_DIRECT
Summary: Add support for Direct I/O in FileChannel
Reviewed-by: alanb, bpb, alanbur, coffeys, aph, clanger, plevart, mli, psandoz, simonis
Contributed-by: Lucy Lu <yingqi.lu@intel.com>, Volker Simonis <volker.simonis@gmail.com>