[LLD] [COFF] Error out if new LTO objects are pulled in after the main LTO compilation (#71337)

Normally, this shouldn't happen. It can happen in exceptional
circumstances, if the compiled output of a bitcode object file
references symbols that weren't listed as undefined in the bitcode
object file itself.

This can at least happen in the following cases:
- A custom SEH personality is set via asm()
- Compiler generated calls to builtin helper functions, such as
__chkstk, or __rt_sdiv on arm

Both of these produce undefined references to symbols after compiling to
a regular object file, that aren't visible on the level of the IR object
file.

This is only an issue if the referenced symbols are provided as LTO
objects themselves; loading regular object files after the LTO
compilation works fine.

Custom SEH personalities are rare, but one CRT startup file in mingw-w64
does this. The referenced pesonality function is usually provided via an
import library, but for WinStore targets, a local dummy reimplementation
in C is used, which can be an LTO object.

Generated calls to builtins is very common, but the builtins aren't
usually provided as LTO objects (compiler-rt's builtins explicitly pass
-fno-lto when building), and many of the builtins are provided as raw .S
assembly files, which don't get built as LTO objects anyway, even if
built with -flto.

If hitting this unusual, but possible, situation, error out cleanly with
a clear message rather than crashing.

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