stackoverflow in 1.4.4 #750

What version of regex are you using?

If it isn't the latest version, then please upgrade and check whether the bug
is still present.

Describe the bug at a high level.

1.4.4 breaks windows build of grpcio.

What are the steps to reproduce the behavior?

Just run cargo test --all on Windows.

What is the actual behavior?

Build fails when generating bindings using rust-bindgen, which uses regex to process sources.

When downgrade regex back to before e040c1b, the build can finish successfully, so the bug is probably introduced by #749.

What is the expected behavior?

It compiles successfully.

What do you expect the output to be?