Use ISO __func__ instead of __FUNCTION__

[andrelucas]

gcc5 complains about FUNCTION.

[kozlovic]

@andrelucas Thank you for your contribution. Unfortunately, I cannot merge this PR as-is: it would fail to compile on Windows (it compiles ok for me on Mac OS/X and Ubuntu).

However, what you could do is replace references of __func__ in this file with __NATS_FUNCTION__, add #include "natsp.h" and in src/include/n-unix.h add #define __NATS_FUNCTION__ __func__ and in src/include/n-win.h add #define __NATS_FUNCTION__ __FUNCTION__.

We could do all that directly in err.h, but doing the way I describe makes this available to other source files where we may need to have access to __func__/__FUNCTION__ in the future.

Let me know if you would like to make those changes, or I can do it if you prefer.

[andrelucas]

I'll gladly do that, thanks for the crystal-clear explanation.

[kozlovic]

@andrelucas All good! Thanks again for the contribution.