[https://github.com/kripken/emscripten/wiki/Tutorial] get the 3.2 version of llvm&clang source (not 3.1, not 3.4, not svn last release...)
[Source] unpack llvm-3.2.src.tar.gz and clang-3.2.src.tar.gz and create an empty build directory with the following structure and names
[Structure] llvm/ llvm/tools/clang/ build/
[Command line] cd build ../llvm/configure --enable-optimized make -j 4 make check-all sudo make install
[Other] add the flag '-Wno-nested-anon-types' for compilation ?