Changes made after `setjmp()` are destroyed and need reassignment.
This problem is now caused by the addition of the `OP_JUW` instruction.

When actually building on FreeBSD 12.1 with `clang10 -fsanitize=address`, mrbtest "NameError#name [15.2.31.2.1]" is failed.

However, qualifying `pc` with `volatile` slows down significantly and increases the object code.
Suppress them by qualifying only the variables that restore `pc`.