Add the PERF_EVENT_IOC_* constants on Linux which are used to
enable/disable/configure perf events. Also add the PERF_IOC_FLAG_GROUP
constant which might be using as part of the ioct argument. See section
"perf_event ioctl calls" in
http://man7.org/linux/man-pages/man2/perf_event_open.2.html

Change-Id: I92fb8f6ef5cc53711f00db566d8e277cdf1cd607
Reviewed-on: https://go-review.googlesource.com/47770Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>