wrapper.py: write macro to optionally print called PENCIL function

The generated wrapper.c files will need to be compiled with
-DSHOW_CALLED_PENCIL_FUNCTIONS to actually print the function names at
runtime.

Change-Id: Id66b13886759390a91ff588b1c454c66b69c68a8
Update VOBLA front-end to respect new PENCIL IR.

Change-Id: I1fcf988af0bf0c058f0d9dd1632f9ec6cf8f01d7