[LLD] [COFF] Fix handling of LTO comdats with nontrivial selection types after 728cc007

Commit 728cc007 made comdat symbols
from LTO objects be treated as any regular comdat symbol. This works
great for symbols that actually are IMAGE_COMDAT_SELECT_ANY, but
if the symbols have a less trivial selection type that require comparing
either the section chunk size or contents, we can't check that before
actually doing the LTO compilation.

Therefore bring back one aspect of handling from before; that comdat
resolution with a leader from an LTO symbol is essentially skipped,
like it was before 728cc007.

Differential Revision: https://reviews.llvm.org/D104605