Debian developer and LLVM/Clang enthusiast Sylvestre Ledru has provided an update regarding the build results for trying to compile the Debian archive using this GCC compiler alternative.

Long story short, when building the Debian package archive under LLVM Clang 5.0 rather than GNU's GCC there is still around a 5% build failure. This is overall an improvement compared to past LLVM/Clang releases, but still not good enough for building the complete Debian archive for a number of reasons.

Among the problems are Clang triggering more warnings/errors than GCC, incompatibilities with GCC switches, and other problems. The developer concludes that "having Debian being built with Clang by default is still a long shot."

More details via this blog post.