I did this on OS X 10.10.5 (14F27) using the 10.10 SDK included in Xcode
6.4 (6E35b). This required removing a C include from mkerrors.sh, since
it doesn't exist on either of my two systems.

I spot checked the syscall number changes against this definitive list,
which is for approximately my kernel version:

    http://www.opensource.apple.com/source/xnu/xnu-2782.20.48/bsd/kern/syscalls.master

Everything I examined checked out, including the removed syscalls being
marked as "old" or being described in comments as no longer existing.

There is one exception to the output being cleanly autogenerated: I have
manually renamed SYS_SYSCTL back to SYS___SYSCTL, the name used
previously and still used by syscall_bsd.go. Because it would distract
from this CL, I will fix this in an upcoming CL.

Change-Id: I0168f608cab714aa5981b3e7d08d8fd84888d0d5
Reviewed-on: https://go-review.googlesource.com/14006Reviewed-by: Ian Lance Taylor <iant@golang.org>