HLSL: Allow arbitrary baseType -> baseType conversion of calling arguments.

This also puts a stake in the ground as to which is better when selection
from multiple signatures.

glslang/MachineIndependent/Intermediate.cpp

@@ -750,6 +750,7 @@ bool TIntermediate::canImplicitlyPromote(TBasicType from, TBasicType to, TOperat
             case EOpDivAssign:               // ... 
             case EOpModAssign:               // ... 
             case EOpReturn:                  // function returns can also perform arbitrary conversions
+            case EOpFunctionCall:            // conversion of a calling parameter
                 return true;
             default:
                 break;