Comment 12 for bug 744595

Since Revision 6319 cmake issues a warning if the compiler is identified as Clang.

The warning text is:

WARNING!!! You seem to compile widelands using the clang/llvm compiler infrastructure. Please note that we do not yet support compiling with clang. You are very likely to run into problems. We are working on it, though. In the mean time, please use GCC infrastructure to compile widelands. You can use the CMake parameter -DCMAKE_CXX_COMPILER=g++ to force GCC if you have it installed. Thank you for your understanding.