arch: fix build under MacOSX put O_DIRECT under ifdefs -- this fixes build for MacOSX. Also use correct class for arm64 openFlagTable.
arch: fix build under MacOSX
put O_DIRECT under ifdefs -- this fixes build for MacOSX.
Also use correct class for arm64 openFlagTable.

Committed by: Nilay Vaish <nilay@cs.wisc.edu>

vovojh/gem5,pombredanne/http-repo.gem5.org-gem5-,vovojh/gem5,vovojh/gem5,pombredanne/http-repo.gem5.org-gem5-,pombredanne/http-repo.gem5.org-gem5-,pombredanne/http-repo.gem5.org-gem5-,pombredanne/http-repo.gem5.org-gem5-,vovojh/gem5,pombredanne/http-repo.gem5.org-gem5-,vovojh/gem5,vovojh/gem5,pombredanne/http-repo.gem5.org-gem5-,vovojh/gem5