Run unit tests with C++ too

[Mattias Rönnblom]

It would be great if the unit test suite (app/test/*) was compiled (and 
run) using a C++ (C++11) compiler as well. At least, if such is available.

With the current state of affairs, header file macros or functions are 
not verified to be functional (or even valid) C++.

"C is a subset of C++", which was never true, is becoming less and less so.

If all unit tests aren't valid C++, maybe one could start with an "opt 
in" model.

A drawback of this is that the unit tests need to be both valid C and 
valid C++.