Fix compilation of panic!() when the arg is another macro.

[celinval]

Description of changes:

In rust, a macro cannot expand another macro that was given as an argument. However, some of the std macros are expanded inside the compiler, which gives them a way around that.

Because we implement those macros are regular macros, we cannot expand other macros and we also cannot limit the first argument to be a literal.

I decided for now to just relax what we accept as the first argument.

Resolved issues:

Resolves #1386

Call-outs:

This solution us to accept whatever the std panic!() macro accepts, but it may accept invalid things as well, such as:

  panic!("invalid" / "division");

That was already accepted as the other arguments of these macros, so I don't think this is big step back. This also won't impact soundness since whatever issue that could rise from creating the expression is inside a panic statement; thus verification has failed already.

Testing:

• How is this change tested? New test + old tests.

• Is this a refactor change? No

Checklist

• Each commit message has a non-empty body, explaining why the change was made
• Methods or procedures are documented
• Regression or unit tests are included, or existing tests cover the modified code
• My PR is restricted to a single feature or bugfix

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 and MIT licenses.