arm_compute v18.03

Change-Id: I8f9a2a9d32a6cab019b8504d313216f28671f9f5
diff --git a/src/runtime/CPP/CPPScheduler.cpp b/src/runtime/CPP/CPPScheduler.cpp
index 4e4dd87..168ed6e 100644
--- a/src/runtime/CPP/CPPScheduler.cpp
+++ b/src/runtime/CPP/CPPScheduler.cpp
@@ -163,7 +163,7 @@
 
 void CPPScheduler::set_num_threads(unsigned int num_threads)
 {
-    _num_threads = num_threads == 0 ? std::thread::hardware_concurrency() : num_threads;
+    _num_threads = num_threads == 0 ? num_threads_hint() : num_threads;
     _threads.resize(_num_threads - 1);
 }