Fix linking error when using concordium_dbg!

Purpose

Fix a linking error when using concordium_dbg! (see https://github.com/Concordium/concordium-rust-smart-contracts/pull/374 for more details on the debug functionality).

When running cargo concordium test --out concordium-out/module.wasm.v1 --allow-debug in the icecream example, I get the following error:

error: linking with `cc` failed: exit status: 1
  |
  = note: LC_ALL="C" PATH="/Users/kasper/.rustup/toolchains/1.72-aarch64-apple-darwin/lib/rustlib/aarch64-apple-darwin/bin
...
s/kasper/.rustup/toolchains/1.72-aarch64-apple-darwin/lib/rustlib/aarch64-apple-darwin/lib" "-o" "/Users/kasper/Developer/Concordium/rust-contracts/examples/fib/target/debug/deps/libfib.dylib" "-Wl,-dead_strip" "-dynamiclib" "-Wl,-dylib" "-nodefaultlibs"
  = note: Undefined symbols for architecture arm64:
            "_debug_print", referenced from:
                concordium_std::debug_print::h1f7e449ccf275907 in libconcordium_std-66bba2a1e91b6971.rlib(concordium_std-66bba2a1e91b6971.15091wxt0levty95.rcgu.o)
          ld: symbol(s) not found for architecture arm64
          clang: error: linker command failed with exit code 1 (use -v to see invocation)

error: could not compile `fib` (lib) due to previous error
Error: Could not build and run integration tests.

The issue is resolved by adding the debug_print dummy host function. I also added the two other methods that were missing. I assume they might cause a similar error if they were triggered.

My initial guess was that the issue only occurred if the tests.rs file imported the lib.rs file, which has the concordium_dbg! calls, but that is not the case; the error also occurs if the smart contract isn't imported in the tests.

Since this hasn't been caught yet, it might only be an issue on macOS.

Changes

Add three missing dummy host calls.

Checklist

[x] My code follows the style of this project.
[x] The code compiles without warnings.
[x] I have performed a self-review of the changes.
[x] I have documented my code, in particular the intent of the hard-to-understand areas.
[x] (If necessary) I have updated the CHANGELOG.

Concordium / concordium-rust-smart-contracts