Implement getloadavg()

v2:
autoload PerfDataHelper functions
Keep loadavg in shared memory
Guard loadavg access by a mutex
Initialize loadavg to the current load

v3:
Shared memory version bump isn't needed if we are only extending it
Remove unused autoload
Mark inititalized flags as NO_COPY for correct behaviour in fork child

Signed-off-by: Jon Turney <jon.turney@dronecode.org.uk>

winsup/cygwin/loadavg.h

@@ -0,0 +1,24 @@
+/* loadavg.h: load average support.
+
+  This file is part of Cygwin.
+
+  This software is a copyrighted work licensed under the terms of the
+  Cygwin license.  Please consult the file "CYGWIN_LICENSE" for
+  details. */
+
+#ifndef LOADAVG_H
+#define LOADAVG_H
+
+class loadavginfo
+{
+  double loadavg[3];
+  time_t last_time;
+
+ public:
+  void initialize ();
+  int fetch (double _loadavg[], int nelem);
+  void update_loadavg ();
+  void calc_load (int index, int delta_time, int decay_time, double n);
+};
+
+#endif /* LOADAVG_H */