Fixes for clang compilation.

The ALTI module uses GNU specific compiler flags that do not work with clang. The fix makes this conditional on the compiler used.

In addition there are gazillion bugs because it uses a C macro calling a variadic C function and passes it C++ objects which is not possible. It seems g++ does not even warn about this, while clang++ considers it rightly an error - the code would have likely crashed when the relevant CERR() code path would have been executed.