Add emit c decl map flag to c2rust wrapper

[Crocodoctopus]

This adds --emit-c-decl-map to the c2rust transpile invocation in C2RustWrapper.

I assume can just inline the flag, as that appears to be the convention already?

[fw-immunant]

Because the --emit-c-decl-map flag places the C decl map alongside the generated Rust sources, I don't think it should be a problem to produce these files even when not strictly desired, but just for cleanliness it might be good to gate this behavior on a corresponding outer Hayroll flag.

I'm also curious, in this case where is the resulting C decl map left for the rest of the CRISP loop, and which preprocessor variant of the C sources does it refer to? I would think we need to merge the C decl map across multiple preprocessed variants of the C sources to include the union of all preprocessor-gated functions/lines, at the very least.