Change default object alignment to 8 bytes. Ensure that the starting
position of the GC top pointer is aligned.
Added an is_reference_type helper function and refactored make_ref to use
this as adding references to environment objects just was not working.
Commenting out the code in lambda.c that removes the return instruction
from the tailcall promotion code as the return is still (unfortunately)
needed for calls to C functions.
Make regular calls work with C functions too. More or less.