rocr: supported_isas map elements should persist

The supported_isas static unordered_map was adding stack
allocated Isa objects. Instead, make the objects statically
allocated, as supported_isas itself is.

Change-Id: I23405e218290d48deea6f984f76c57e7b43e314e

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

@@ -226,7 +226,7 @@ class IsaRegistry final {
 
  private:
   /// @brief IsaRegistry's map type.
-  typedef std::unordered_map<std::string, Isa> IsaMap;
+  typedef std::unordered_map<std::string, std::reference_wrapper<const Isa>> IsaMap;
 
   /// @brief  Default constructor
   IsaRegistry() = delete;