The swig.gdb file provides the swigprint and locswigprint user-defined
commands which stopped working somewhere around gdb 8.0 - 8.2.
```
(gdb) swigprint n
Undefined command: "Printf". Try "help".
(gdb) locswigprint n
Undefined command: "Printf". Try "help".
(gdb)
```
I couldn't find any mention of gdb's Printf, but replacing Printf with
printf works and is documented at
https://sourceware.org/gdb/download/onlinedocs/gdb/Output.html#Output
Fixes issue #1420
[skip ci]
