[test-suite] Fix CLAMR build with glibc 2.32+

[kito-cheng]

Summary

sys/sysctl.h has been removed at glibc 2.32, so this header should
not used anymore, however sysctl still invoked at memstats_memtotal,
but only for invoked when APPLE_CC is defined.

So moving #include <sys/sysctl.h> into #ifdef __APPLE_CC__.

[kito-cheng]

News of Glibc 2.32:
https://sourceware.org/pipermail/libc-announce/2020/000029.html

* The deprecated <sys/sysctl.h> header and the sysctl function have been
  removed.  To support old binaries, the sysctl function continues to
  exist as a compatibility symbol (on those architectures which had it),
  but always fails with ENOSYS.  This reflects the removal of the system
  call from all architectures, starting with Linux 5.5.

[kito-cheng]

I don't know who is the right people to add as reviewer here, and I saw @MaskRay and @lenary you guys has reviewed this repo before, and most important is I know you guys :P so could you help me to review that or find the right people to review that? Thanks :)

[MaskRay]

Looks great!

MultiSource/Benchmarks/DOE-ProxyApps-C++/CLAMR/memstats.c

  *           David Nicholaeff        [e-mail], [e-mail]
  *           Dennis Trujillo         [e-mail], [e-mail]
  * 
  */
 #include <sys/time.h>
 #include <stdlib.h>
 #include <stdio.h>
 #include <sys/types.h>
-#include <sys/sysctl.h>
 #include <unistd.h>
 #include <string.h>
 
 #ifdef __APPLE_CC__
+#include <sys/sysctl.h>
 #include <mach/mach_host.h>
 #include <mach/task.h>
 #endif
 
 #ifdef HAVE_CONFIG_H
 #include "config.h"
 #endif