unix: add taskstats type and constants on Linux

Taskstats is a netlink-based interface for sending per-task and
per-process statistics from the kernel to userspace.

For more information, please see:
https://www.kernel.org/doc/Documentation/accounting/taskstats.txt.

Fixes golang/go#21616.

Change-Id: I7d4b8035aa8e993074d61911d9a8c3a3e61c9b2e
Reviewed-on: https://go-review.googlesource.com/59050
Run-TryBot: Matt Layher <mdlayher@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

unix/mkerrors.sh

@@ -181,6 +181,7 @@ struct ltchars {
 #include <linux/serial.h>
 #include <linux/can.h>
 #include <linux/vm_sockets.h>
+#include <linux/taskstats.h>
 #include <net/route.h>
 #include <asm/termbits.h>
 
@@ -413,6 +414,7 @@ ccflags="$@"
 		$2 ~ /^SECCOMP_MODE_/ ||
 		$2 ~ /^SPLICE_/ ||
 		$2 ~ /^(VM|VMADDR)_/ ||
+		$2 ~ /^(TASKSTATS|TS)_/ ||
 		$2 ~ /^XATTR_(CREATE|REPLACE)/ ||
 		$2 !~ "WMESGLEN" &&
 		$2 ~ /^W[A-Z0-9]+$/ ||