stats: avoid cgo in collector

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>
(cherry picked from commit cf104d85c35947c25dcd86cef19aa97fe31e4bbd)
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

daemon/stats/collector_unix.go

@@ -9,13 +9,9 @@ import (
 	"strings"
 
 	"github.com/opencontainers/runc/libcontainer/system"
+	"golang.org/x/sys/unix"
 )
 
-/*
-#include <unistd.h>
-*/
-import "C"
-
 // platformNewStatsCollector performs platform specific initialisation of the
 // Collector structure.
 func platformNewStatsCollector(s *Collector) {
@@ -70,13 +66,10 @@ func (s *Collector) getSystemCPUUsage() (uint64, error) {
 }
 
 func (s *Collector) getNumberOnlineCPUs() (uint32, error) {
-	i, err := C.sysconf(C._SC_NPROCESSORS_ONLN)
-	// According to POSIX - errno is undefined after successful
-	// sysconf, and can be non-zero in several cases, so look for
-	// error in returned value not in errno.
-	// (https://sourceware.org/bugzilla/show_bug.cgi?id=21536)
-	if i == -1 {
+	var cpuset unix.CPUSet
+	err := unix.SchedGetaffinity(0, &cpuset)
+	if err != nil {
 		return 0, err
 	}
-	return uint32(i), nil
+	return uint32(cpuset.Count()), nil
 }