Cppcheck exits with code 0 (success) despite errors

[shameekganguly]

Environment

• OS Version: All
• Source build

Description

• Expected behavior: make cppcheck should return non-zero exit code if any error is detected.
• Actual behavior: Cppcheck exits with return code of 0. See recent CI run in gz-sim for e.g. https://github.com/gazebosim/gz-sim/actions/runs/10464654584/job/28978620348 shows

/github/workspace/include/gz/sim/Conversions.hh:636:7: error: Found a exit path from function with non-void return type that has missing return statement [missingReturn]
        Out::ConversionNotImplemented;

But the exit code was 0, so CI passed.

Looks like cppcheck requires the --error-exitcode=<n> cmdline arg to be set in order to exit with a non-zero code in case of error. This will need to be set in cmake/GzCodeCheck.cmake to catch errors in CI.