[Toybox] xcount_cpus

[enh]

bionic had to give up on using /proc/cpuinfo or /proc/stat for
counting cpus. in particular, a certain soc vendor rob's worked for in
the past insists on doing things wrongly. the only methods we've never
had problems with on any kernel on any architecture are:

if you want online cpus, parse /sys/devices/system/cpu/online.

if you want offline cpus too, count cpu\d+ entries in /sys/devices/system/cpu.

is there a reason why you don't just use sysconf(3) and let it be the
C library's problem? (if so, that's probably worth a code comment.)

-- 
Elliott Hughes - http://who/enh - http://jessies.org/~enh/
Android native code/tools questions? Mail me/drop by/add me as a reviewer.

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