It has annoying downsides like the need to setup a complete "project" with build options and all -- goodbye "build system is enough".
It's almost surely unique to libclang, but a "build system is enough" is actually accurate. The libclang API can read so-called "[compilation database](http://clang.llvm.org/docs/JSONCompilationDatabase.html)" (a simple JSON file) which is designed to be generated by the build system so there's nothing extra to configure. I know at least CMake supports generating the compilation database and I don't expect it to be terribly difficult to add support to an Autotools build system, or using something like [Bear](https://github.com/rizsotto/Bear) for Autotools or plain make.