unix: don't use deprecated sys/capability.h header on FreeBSD

sys/capability.h is deprecated, use sys/capsicum.h instead.

Change-Id: I05a3b8ff28d4df6536a3f10e0da7381b48329738
Reviewed-on: https://go-review.googlesource.com/c/147737
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

unix/mkerrors.sh

@@ -101,7 +101,7 @@ includes_DragonFly='
 '
 
 includes_FreeBSD='
-#include <sys/capability.h>
+#include <sys/capsicum.h>
 #include <sys/param.h>
 #include <sys/types.h>
 #include <sys/event.h>

unix/types_freebsd.go

@@ -26,7 +26,7 @@ package unix
 #include <termios.h>
 #include <stdio.h>
 #include <unistd.h>
-#include <sys/capability.h>
+#include <sys/capsicum.h>
 #include <sys/event.h>
 #include <sys/mman.h>
 #include <sys/mount.h>