Regression: tree shaking wrong when var declaration+assignment is inside a conditional

[nifgraup]

• Rollup Version: 0.68.1
• Operating System (or Browser): Linux
• Node Version: v8.9.3

How Do We Reproduce?

test.js

// example 1
switch (test) {
  case 1:
    var hoisted = true;
  case 2:
    if (hoisted) console.log('Went also through  case 1.');
}

// example 2
if (x) {
  var h2 = true;
}
if (h2) console.log('x is true');

./bin/rollup --format cjs test.js

Expected Behavior

no tree shaking

Actual Behavior

'use strict';

// example 1
switch (test) {
  case 1:

  case 2:
    console.log('Went also through  case 1.');
}
console.log('x is true');

Regression point 187a256

[lukastaegert]

This was fixed via #2607 in Rollup@0.68.2