[lld-macho]Allow folding entries with identical FDE (#216895)
This is done by normalising the embedded reloc data before doing a
comparison in ICF.
(Context: see https://github.com/llvm/llvm-project/pull/213778, which
proposed this idea but with a different implementation approach)
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Co-authored-by: Ellis Hoag <ellis.sparky.hoag@gmail.com>