#281 Put checks in owllink.h for unsupported combinations of settings

[Ognyan Chernokozhev]

Recently a problem with C++ Builder build turned out to be by a misconfigured project that was using unsupported combination of settings. See discussion https://sourceforge.net/p/owlnext/discussion/97175/thread/cd1d231e4d/.

Ideally the owllink.h can have checks for such bad combinations of settings and issue clear compile-time errors.

The known bad setting is not having multi-threading correctly setup for C++ Builder Clang compilation.