posix/sched_cpucount.c assumes that size of __cpu_mask == size of long,
which is incorrect for x32. This patch uses __builtin_popcount, which
is availabe in GCC 4.9, in posix/sched_cpucount.c.
Tested on i686, x86-64 and x32 with multi-arch disabled.
[BZ #21696]
* posix/sched_cpucount.c: Don't include <limits.h>.
(__sched_cpucount): Use __builtin_popcount.
(tests): Add tst-cpucount.
* posix/sched_cpucount.c: New file.
* posix/tst-cpucount.c: New file.
* posix/Versions: Export __sched_cpucount with version GLIBC_2.6.