Issue Description:

The following code causes a memory leak:

func foo() {
  struct A {
    var a = "hello"
    var b = B()
    struct B {
      var c = "world"
    }
  }

  if case (_?, _)? = Mirror(reflecting: [A()]).children.first {
  }
}

Call foo() from the body of a SwiftUI app, in applicationDidFinishLaunching, a main.swift executable, etc., to see. Then run the app, open the memory graph debugger, and you will see a 48 byte malloc leak.

The layout of type A, the reflection on an array of the same type and the destructuring pattern all seem to contribute to the leak. If any of these things changes slightly, the leak goes away.