Fix an error where a GCStackRoot was being passed to make_pair(), causing
destructors to run in incorrect order.
Replace use of boost::bind that doesn't compile under C++11 with mem_fun.
Enable byte-compiled functions to be JIT compiled to native code.

This works by extracting the AST form that the byte-compiled function was
built from, and compiling that.  It does not JIT compile the bytecode.
Add the llvm libraries to the main LIBS variable, so they get included whenever
needed.
Comment out a test that does nothing except to allocate a _16GB_ numeric vector.