With the supported compilers, we can't rely on the return value of snprintf()
and historically have replaced it with safe_snprintf().  For macOS however,
snprintf() is apparently a macro, not a function, so gendefs.h throws and
error due to redefinition.

Rather than hack around on that, just ensure that we never use the return
value of snprintf() and use safe_snprintf() to ensure we know what the
return value will be.