Compilation error (macOS): unused parameter

[harkabeeparolus]

Compilation error on macOS Catalina 10.15.5:

utils.c:372:62: error: unused parameter 'completions' [-Werror,-Wunused-parameter]
getstring_with_completion(char *prompt, const char * const * completions)
                                                             ^
1 error generated.

The error seems happen since the usage of the parameter completions is hidden by an ifdef:

#ifdef HAS_READLINE
        completion_values = completions;
[...]

• Apple clang version 11.0.0 (clang-1100.0.33.17)
• Target: x86_64-apple-darwin19.5.0

[heirecka]

Duplicate of #10