unix: add perf event ioctl constants on Linux

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/47770
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

unix/linux/types.go

@@ -47,6 +47,7 @@ package unix
 #include <linux/filter.h>
 #include <linux/keyctl.h>
 #include <linux/netlink.h>
+#include <linux/perf_event.h>
 #include <linux/rtnetlink.h>
 #include <linux/icmpv6.h>
 #include <asm/termbits.h>
@@ -533,6 +534,8 @@ type Sigset_t C.sigset_t
 
 const RNDGETENTCNT = C.RNDGETENTCNT
 
+const PERF_IOC_FLAG_GROUP = C.PERF_IOC_FLAG_GROUP
+
 // sysconf information
 
 const _SC_PAGESIZE = C._SC_PAGESIZE