Report call to unknown function
Report call to unknown function

The compiler doesn't error out, but will emit a call to a function
with id 0.  I don't know how to error out from within the code
generator.

This will make it easier to debug the case where we are missing
support for a builtin.

google/clspv,google/clspv,google/clspv,google/clspv,google/clspv