main/openssl: change to "linux-x86-latomic" target

Upstream suggests that "linux-elf" is for compatibility with ancient compilers.

https://github.com/openssl/openssl/blob/a46abbd66eecdbfba84c81eca8911f5d9564c8a8/Configurations/10-main.conf#L840

Marked as draft because I didn't get to test it yet, my 32bit x86 machine is busy trying to bootstrap aarch64, which takes a while on hardware of this vintage 😆