A linkonce_odr definition can be omitted in LTO compilation if
`canBeOmittedFromSymbolTable()` is true in all bitcode files.

Currently, we don't respect the `canBeOmittedFromSymbolTable()` bit from
symbols in a non-prevailing COMDAT, which could lead to incorrect
omission of a definition when merging a prevailing linkonce_odr and a
non-prevailing weak_odr, e.g. an implicit template instantiation and an
explicit template instantiation.

To fix #111341, allow the non-prevailing COMDAT code path to clear the
`ltoCanOmit` bit, so that `VisibleToRegularObj` could be false in
LTO.cpp. We could resolve either an Undefined or a Defined. For
simplicity, just use a Defined like the prevailing case (similar to how
we resolve symbols in ObjectFile COMDAT reviews.llvm.org/D120626).

Pull Request: https://github.com/llvm/llvm-project/pull/119332

This reverts commit 2b129dacdde667137b5012d52f1d96e0ab26c749.

parseSymbolVersion can be combined with computeIsPreemptible,
making hasVersionSyms unneeded.

We can just scan objectFiles and sharedFiles that have versioned symbols
to skip scanning the global symtab. While we won't suggest __wrap_foo
for undefined __wrap_foo@v1 when --wrap=foo@v1 is specified
(internalFile isn't scanned), this edge case difference is acceptable.

When computing whether a defined symbol is exported, we set
`exportDynamic` in Defined and CommonSymbol's ctor and merge the bit in
symbol resolution. The complexity is for the LTO special case
canBeOmittedFromSymbolTable, which can be simplified by introducing a
new bit.

We might simplify the state by caching includeInDynsym in exportDynamic
in the future.

After #78944 and some follow-ups, sym->file, unless in the initial
Placeholder stage, is guaranteed to be non-null.

and reorder sh_type checks to make SHT_PROGBITS/SHT_GROUP fast.