Patch from github.

At the moment it is not possible to build ROCr with Clang. This is
a spurious limitation. The present PR addresses it by guarding GCC
only flags and by fixing some additional warnings that Clang triggers;
one of said warnings did outline a rather interesting issue with math
being done on void*s. - AlexVlx

Void ptr arithmetic had already been fixed in amd-master branch.

Change-Id: I5ee97e20b5c40b10dd73facecabe75f02ba46462

runtime/hsa-runtime/core/inc/host_queue.h

@@ -162,7 +162,7 @@ class HostQueue : public Queue {
   void operator delete(void*, void*) {}
 
  protected:
-  bool _IsA(Queue::rtti_t id) const { return id == &rtti_id_; }
+  bool _IsA(Queue::rtti_t id) const override { return id == &rtti_id_; }
 
  private:
   static int rtti_id_;