Fix runtime C maybe benchmark example

[paulcadman]

The constr_info_t struct has changed, so this example must be changed accordingly.

The benchmark builds are still broken because I missed this file in #2192

I've removed the unsupported wasm target from the compile.sh script in the benchmark directory to make it easier to spot errors.

[lukaszcz]

How do the benchmarks compile when doing the benchmarks? They don't use compile.sh? Now the WASM target name is wasm32-wasi.

[paulcadman]

How do the benchmarks compile when doing the benchmarks? They don't use compile.sh? Now the WASM target name is wasm32-wasi.

The benchmarks don't use compile.sh, the compiler invocations are defined in https://github.com/anoma/juvix/blob/main/bench/Variants.hs. However there is no way of compiling all the benchmark examples without running the benchmark suite, which takes several hours. The compile.sh script is useful for sanity checking the examples.