cargo: Add rustflag to force frame pointers

[har7an]

as required by the
esp-backtrace crate.

[har7an]

I found this after inspecting the esp-backtrace crate, which was included as dependency in a new project I generated from the no_std template today. Although I must say that it also works without this flag, and the output is the same regardless of whether it is present or not (for Panics, that is. Haven't tested exceptions yet).

[MabezDev]

Frame pointers make no difference on Xtensa, the ABI guarantees access to the previous frame. This PR should be adding the flag in the RISC-V section. On top of that we should probably add a comment next to it mentioning that although you get better debuggability, the code produced is most likely sub-optimal.

[har7an]

I see, thanks for clarifying!
Should I still add it by default then, or maybe commented out with the explaining comment next to it? I'll also try to file a PR against esp-backtrace to add that bit of information to the README.

[MabezDev]

imo we should add it by default, I personally value debuggability over performance when developing applications. As long as we mention that for production builds you probably want to turn this off (possibly even then not, if you want to send backtraces to the cloud) it should be okay.

[har7an]

Done, what do you think?

[MabezDev]

Perfect, thanks!

[bjoernQ]

LGTM - Thanks!