Translate goto label attached to switch case

[lucic71]

Translates a label atttached to a switch case, from:

  switch (n) {
  target:
  case 0:
    ...
  case 1:
    ...
    goto target;

to

    switch!(match n {
        __v if __v == 0 => 'target: {
            ...
        }
        __v if __v == 1 => {
            ...
            goto!('target);
        }

To make this work, I refactored all switch-analysing functions into a single struct, called SwitchArm. Now, VisitSwitchStmt first calls AnalyzeSwitchArms, then iterates over the SwitchArms and generates the corresponding Rust code. Each SwitchArm has a field called label used for generating __v if __v == 0 => 'target: {, i.e. a labeled block in Rust.

The changes in libcc2rs-macros/src/switch.rs are minimal. I added support for accepting a labeled block in the switch! macro.

[nunoplopes]

you can use emplace_back without {} (more efficient, constructs in place)

[lucic71]

Done