CMake

> I'm not sure what you mean by databases of systems and features... I didn't really mean a literal database. I meant stuff like this: https://github.com/Kitware/CMake/blob/master/Modules/FindQt4... This is pretty typical CMake. It's encoding that for a particular version of Qt, add a few more compilation flags. It's a "knowledge base" of Qt versions encoded as a CMake module. The autoconf way would be to try to link a minimal program to Qt, and if it fails, try to see if adding more libraries makes the linking succeed. Or this, for example: https://github.com/Kitware/CMake/blob/master/Modules/FindOpe... It is trying to account for two popular compilers on Windows but not with Cygwin. It's the whole chain of "if Windows, if cygwin, if mingw, if msvc" what I called a "database" above. Doesn't clang work on Windows these days? What will thi