A few system call numbers on x86 Linux are
defined in terms of a previous definition,

e.g.,
	#define __NR_timer_create	259
	#define __NR_timer_settime	(__NR_timer_create+1)
	...
	#define __NR_mq_open		277
	#define __NR_mq_unlink		(__NR_mq_open+1)

This change assumes the numbers are sorted
sequentially in the input file.

R=rsc, bradfitzwork
CC=golang-dev
https://golang.org/cl/3946041