I'm getting this error when trying to build Mesa with llvm 3.8.

checking for llvm-config... /usr/lib/llvm-3.8/bin/llvm-config
Package libomxil-bellagio was not found in the pkg-config search path.
Perhaps you should add the directory containing `libomxil-bellagio.pc'
to the PKG_CONFIG_PATH environment variable
No package 'libomxil-bellagio' found
checking for RADEON... yes
configure: error: Could not find llvm shared libraries:
        Please make sure you have built llvm with the --enable-shared option
        and that your llvm libraries are installed in /usr/lib/llvm-3.8/lib
        If you have installed your llvm libraries to a different directory you
        can use the --with-llvm-prefix= configure flag to specify this directory.
        NOTE: Mesa is attempting to use llvm shared libraries by default.
        If you do not want to build with llvm shared libraries and instead want to
        use llvm static libraries then add --disable-llvm-shared-libs to your configure invocation and rebuild.

LLVM is installed in the correct directory (/usr/lib/llvm-3.8).

This error doesn't occur with LLVM 3.7 and the same options.

LLVM is build wih --enable-shared from here (debian snapshot): 
http://llvm-jenkins.debian.net/view/Debian%20unstable/