[EH] Improve catch validation (#4315)

This improves validation of `catch` bodies mostly by checking the
validity of `pop`s.

For every `catch` body:
- Checks if its tag exists
- If the tag's type is none:
  - Ensures there shouldn't be any `pop`s
- If the tag's type is not none:
  - Checks if there's a single `pop` within the catch body
  - Checks if the tag type matches the `pop`'s type
  - Checks if the `pop`'s location is valid

For every `catch_all` body:
- Ensures there shuldn't be any `pop`s

This uncovers several bugs related to `pop`s in existing tests, which
this PR also fixes.

1 files changed, 2 insertions, 0 deletions

diff --git a/src/ir/iteration.h b/src/ir/iteration.h
index b3553f1ec..29d183678 100644
--- a/src/ir/iteration.h
+++ b/src/ir/iteration.h
@@ -53,6 +53,8 @@ template<class Specific> class AbstractChildIterator {
       return index != other.index || &parent != &(other.parent);
     }
 
+    bool operator==(const Iterator& other) const { return !(*this != other); }
+
     void operator++() { index++; }
 
     Expression*& operator*() {