[ELF] Avoid wrapping unreferenced lazy symbols

There's a couple of motivations here:
* LLD 12 (which I was originally testing with) was adding an undefined
  symbol to the symbol table if you attempted to wrap an unreferenced
  lazy symbol, which would later break `--no-allow-shlib-undefined`. LLD
  on main actually produces a weak undefined symbol, so this doesn't
  break anyway, but it's cleaner to not have the weak undefined symbol
  as well. The new behavior also matches bfd and gold.
* PROVIDE in a linker script referencing a wrapped symbol would think
  that an otherwise-unreferenced lazy symbol which was wrapped was
  actually referenced, and therefore proceed with the definition, which
  goes against expectations. The new behavior also matches bfd and gold.

Reviewed By: MaskRay

Differential Revision: https://reviews.llvm.org/D118756