Another possible option for SSL library: https://www.bearssl.org
It at least compiles with PCC, and also with gcc -std=c89 if I remove inline from all the declarations
I was somewhat concerned about the last release being in 2018, but looking at their GitWeb, looks like it's still maintained, just there's not much to do
No TLS 1.3, but 🤷 it'd be nice if things worked at all, I hope that websites keep around TLS 1.2 for a long time