[lld-macho] Emit personalities in compact unwind

[lld-macho] Emit personalities in compact unwind

Note that there is a triple indirection involved with
personalities and compact unwind:

1. Two bits of each CU encoding are used as an offset into the
   personality array.
2. Each entry of the personality array is an offset from the image base.
   The resulting address (after adding the image base) should point within the
   GOT.
3. The corresponding GOT entry contains the actual pointer to the
   personality function.

To further complicate things, when the personality function is in the
object file (as opposed to a dylib), its references in
`__compact_unwind` may refer to it via a section + offset relocation
instead of a symbol relocation. Since our GOT implementation can only
create entries for symbols, we have to create a synthetic symbol at the
given section offset.

Reviewed By: clayborg

Differential Revision: https://reviews.llvm.org/D95809