You can now build with both the internal (patched) LLVM 2.7,
or an external LLVM 2.8rc.
To build with external do this:
./configure --enable-llvm --with-system-llvm=/path/to/llvm-config
This will link against the external LLVM's .a files (they are PIC), so
LLVM will stay only a build time dependency.
Török Edvin