(time_function): Use clock_gettime with CLOCK_PROCESS_CPUTIME_ID,
if available. This gives better accuracy, at least on recent
linux.
+ (BENCH_INTERVAL): Reduced to 0.1 s.
+ (struct bench_memxor_info): New struct.
+ (bench_memxor): New function.
+ (time_memxor): New function.
+ (main): Use time_memxor. Added optional argument used to limit the
+ algorithms being benchmarked.
* examples/Makefile.in (nettle-benchmark): Link using
$(BENCH_LIBS) rather than $(LIBS).