unix: add watchdog constants on Linux

To be used e.g. in
https://github.com/gokrazy/gokrazy/commit/2e60d5b8c8c35e0eed1bb155c7d709c729c8f041

Change-Id: If79ffec9021dc79375c861a0ddd9dd443adb4692
Reviewed-on: https://go-review.googlesource.com/72375
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

unix/mkerrors.sh

@@ -184,6 +184,7 @@ struct ltchars {
 #include <linux/vm_sockets.h>
 #include <linux/taskstats.h>
 #include <linux/genetlink.h>
+#include <linux/watchdog.h>
 #include <net/route.h>
 #include <asm/termbits.h>
 
@@ -422,6 +423,7 @@ ccflags="$@"
 		$2 ~ /^GENL_/ ||
 		$2 ~ /^UTIME_/ ||
 		$2 ~ /^XATTR_(CREATE|REPLACE)/ ||
+		$2 ~ /^WDIOC_/ ||
 		$2 !~ "WMESGLEN" &&
 		$2 ~ /^W[A-Z0-9]+$/ ||
 		$2 ~ /^BLK[A-Z]*(GET$|SET$|BUF$|PART$|SIZE)/ {printf("\t%s = C.%s\n", $2, $2)}