Fix ExceptionPackage memory errors (#3088)

First, adds an explicit destructor call to fix a memory leak in
`Literal::operator=` in which existing `ExceptionPackage`s would be
silently dropped. Next, changes `Literal::getExceptionPackage` to
return the `ExceptionPackage` by value to avoid a use-after-free bug
in the interpreter that was surfaced by the new destructor call.

A future improvement would be to switch to using `std::variant`.

Fixes #3087.

1 files changed, 1 insertions, 4 deletions

diff --git a/src/literal.h b/src/literal.h
index 5c72bf96c..cffa9ab7d 100644
--- a/src/literal.h
+++ b/src/literal.h
@@ -135,10 +135,7 @@ public:
     assert(type == Type::funcref);
     return func;
   }
-  const ExceptionPackage& getExceptionPackage() const {
-    assert(type == Type::exnref);
-    return *exn.get();
-  }
+  ExceptionPackage getExceptionPackage() const;
 
   // careful!
   int32_t* geti32Ptr() {