`prusti_assert` macros incorrect expansion during normal compilation

[Patrick-6]

The following example works when verified by Prusti, but fails when compiled with rustc:

use prusti_contracts::*;

fn test(x: i32) {
    match x {
        0 => prusti_assert!(x == 0), // <== Error here
        _ => assert!(x != 0)
    }
}

The error is:

expected expression, found end of macro arguments

prusti_assert_eq and prusti_assert_ne seem to have the similar problem:

fn test_2(x: i32) {
    match x {
        0 => prusti_assert_eq!(x, 0),
        _ => prusti_assert_ne!(x, 0)
    }
}

macro expansion ends with an incomplete expression: expected expression
the macro call doesn't expand to an expression, but it can expand to a statement.
add `;` to interpret the expansion as a statement: `;`

Expanding the macros to () should fix this.