Add mechanism to lower generic pointers returned by functions

This change introduces a mechanism to lower functions returning generic
pointer to functions returning non-generic pointer.

The mechanism iterates thorugh functions in down-top order (starting from
most nested functions). Once a return type for particular function gets
changed to non-generic, then regular GAS resolver is triggered on all
functions calling updated function to propagate the non-generic pointer.

Author: aratajew

IGC/AdaptorOCL/UnifyIROCL.cpp

@@ -444,6 +444,8 @@ static void CommonOCLBasedPasses(
             mpm.add(createLowerGPCallArg());
         }
 
+        mpm.add(createGASRetValuePropagatorPass());
+
         // Run another round of constant breaking as GAS resolving may generate constants (constant address)
         mpm.add(new BreakConstantExpr());
     }