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/libamdhsacode/amd_options.hpp

@@ -422,7 +422,7 @@ private:
   /// @brief Not copy-assignable.
   PrefixOption& operator =(const PrefixOption&);
 
-  bool ProcessTokens(std::list<std::string> &tokens);
+  bool ProcessTokens(std::list<std::string>& tokens) override;
 
   std::string::size_type FindPrefix(const std::string& token) const;