Linker error due to undefined rust_begin_unwind when creating an importlib on Windows

[urschrei]

I'm generating an importlib using latest stable on Appveyor using -C target-cpu=native -C link-args=-Wl,--out-implib,polylabel.a, but switching from dylib to cdylib now causes a linker error, saying there's an undefined reference to rust_begin_unwind. The crate isn't #![no_main] \ #![no_std], and I'm not doing anything unusual AFAIK.

[Mark-Simulacrum]

I believe this is #18807 based on discussion in #38281, so closing in favor of #18807. See #38281 (comment).