Fix bug in ForceLN.
Fix bug: prologue should only be added once per function.
Eliminate phi nodes by copying.
Correctly report read / written list for StoreWordLN.
Fix bug in genAssertTag.

We don't load the object header to check an objects type -- we infer it
from the tag bits in the object _handle_.
Correctly handle inlined forcing logic.

Fix bug in the way the basic-blocks and labels are handled.
Ensure the final result is forced.

Without this change the result of the program (+ 2 3) is simply a thunk.
Fix calling convention.

x86-64 passes the first argument in %rdi, not %rsi.
Eliminate phi's by inserting copy instructions.
Add inline comments to the generate assembly.

Right now the comments contain the LNode that was lowered, but we will
store more useful information there in the future.
Make ratorIntToConstant respect tag bits.
Fix bug in genAssertTag.

When checking ClsrTagC, we need to bitwise & with ClsrTagC, not 3.