In late 2011 I wrote about LLVM/Clang being able to build LibreOffice. While the open-source compiler could build this popular open-source office suite, the produced binary by this GCC alternative was non-functioning at that time. In the past year and a half, improvements have been made to both LibreOffice and LLVM/Clang.
A Phoronix reader (tip of the hat to "ultimA"), there was an update to Clang'ing LibreOffice in January that went unnoticed on the DocumentFoundation.org Wiki. LLVM 3.1 should be able to handle building LibreOffice and the Clang compiler issues should be worked out in Clang 3.2. Basically, an upstream LLVM/Clang should be able to compile a working LibreOffice (at least LibreOffice 3.6 and presumably the latest upstream, there's no word on the Wiki page if the upstream office improvements are still present in the latest release).
While LLVM/Clang 3.2 is the latest stable release, LLVM/Clang 3.3 is coming in June with even more enhancements. There's some striking performance improvements, C++11 improvements, new CPU support, and much more.