Function is rewritten in C in compiler.d to remove a dependency
between the bytecodes compiler and the clos module. It may be more
performant thanks to more precise type handing, however we use a list
instead of a hashtable, so it may be slower with lookup. To assess
that we should run some benchmarks against real code -- rewriting C
code to work with a hash table should be trivial.
clos::need-to-make-load-form-p is now si::need-to-make-load-form-p and
may be called from C code as si_need_to_make_load_form_p.