update perf_event_open() for Linux 3.11 release

Update the perf_event_open syscall support for new ABIs added
in the 3.11 release.

Thankfully this is pretty minor.  Lots of big changes to the ABI
seem to be afoot for 3.12 though.

Signed-off-by: Vince Weaver <vincent.weaver@maine.edu>
Add MAP_32BIT for x86-64 to mmap flags