separate printf declaration for vdi/clang

There are now two implementations of printf in HIP:

1. The implemenation for HCC is controlled by the HC_FEATURE_PRINTF
   macro, and it works only with the HCC compiler used in combination
   with the HCC runtime.

2. The implementation for hip-clang requires the VDI runtime, and is
   always enabled with that combination.

hipamd/bin/hipcc

@@ -133,6 +133,7 @@ if (defined $HIP_RUNTIME and $HIP_RUNTIME eq "VDI" and !defined $HIP_VDI_HOME) {
     } else {
         $HIP_VDI_HOME = $HIP_PATH; # use HIP_PATH
     }
+    $HIPCXXFLAGS .= "-D__HIP_VDI__";
 }
 
 if (defined $HIP_VDI_HOME) {