Fix calling debuginfo-less functions in Ada

Fix calling debuginfo-less functions in Ada

A co-worker at AdaCore noticed that calling a function without
debuginfo yields:

(gdb) print plus_one(23)
'pck.plus_one' has unknown return type; cast the call to its declared return type

However, this also happens if you follow the directions and add the
cast.

This patch fixes the problem and adds a regression test.