llvm: fix lowering of non-byte-aligned field pointers

* When a field starts at some bit offset within a byte you need to load
   starting from that byte and shift, not starting from the next byte,
   so a rounded-down divide is required here, not a rounded-up one.
 * Remove paragraph from doc that no longer relates to anything.

Closes #12363
f9192adabaJacob Young committed on 10/15/2022, 6:19:40 PM· committed by Andrew Kelleyparentc7f9833
2 files changedLine totals unavailable