(Short question) What's the meaning of the number in those libgcc-s[124]-*-cross packages

[DannyNiu <dannyniu@hotmail.com>]

Greetings.

I have some question on my mind.

I’m writing a Dockerfile for creating a environment for testing
softwares on multiple architectures using the cross-compilation
toolchains available from the OS distribution.

Because those are C programs, I need to link with the libgcc library.
To make sure my Dockerfile can adapt itself over time, I’m
referencing virtual packages in `apt`, and libgcc virtual packages
have those -s1 -s2 and -s4 infixes in their package name.

What do those numbers mean? Is there a wiki page that explain this?
When did Debian developers decide to adopt such numbering?

Thanks.