tests: (re)build test elfs before snapshot tests

[Lotterleben]

not an issue, but a feature request:

currently, the elf files we're using for snapshot tests are pre-compiled. That makes them cumbersome to reproduce, understand or create new ones.

a possible hurdle while implementing this is that the paths printed in backtraces would then vary depending on who's executing the tests– this would have to be either parsed out during test result collection or compiled with --remap-path-prefix

[Lotterleben]

for the record, I've pushed the code I've used to generate the ELFs we're using so far into this repo