Re: using undeclared function returning bool results in wrong return value

[Florian Weimer via Gcc]

* Jonathan Wakely via Gcc:

> Declare your functions. Don't ignore warnings.

It's actually a GCC bug that this isn't an error.  However, too many
configure scripts would still break if we changed the default.

So either use -Werror=implicit-function-declaration or C++ for the time
being.

Thanks,
Florian