proc: for optimized functions allow .closureptr to not exist (#3808)

* proc: flag variables correctly when range-over-func stmts are used

Argument variables of a range-over-func body closure should be returned
flagged as normal local variables, not as function arguments.

Updates #3806

* proc: for optimized functions allow .closureptr to not exist

For optimized functions .closureptr is sometimes omitted from DWARF,
allow it to be 0 and try to recover the range-over-func stack by best
effort.

Fixes #3806

_fixtures/setiterator.go

@@ -0,0 +1,51 @@
+package main
+
+import (
+	"fmt"
+	"iter"
+	"strconv"
+	"time"
+)
+
+func main() {
+	set := New[string]()
+	for i := 10; i < 100; i++ {
+		set.Add(strconv.Itoa(i))
+	}
+	PrintAllElements[string](set)
+}
+
+// Set holds a set of elements.
+type Set[E comparable] struct {
+	m map[E]struct{}
+}
+
+// New returns a new [Set].
+func New[E comparable]() *Set[E] {
+	return &Set[E]{m: make(map[E]struct{})}
+}
+
+// All is an iterator over the elements of s.
+func (s *Set[E]) All() iter.Seq[E] {
+	return func(yield func(E) bool) {
+		for v := range s.m {
+			tmp := make([]byte, 1024)
+			str := string(tmp)
+			if !yield(v) {
+				return
+			}
+			go func() { println(str) }()
+		}
+	}
+}
+
+func (s *Set[E]) Add(v E) {
+	s.m[v] = struct{}{}
+}
+
+func PrintAllElements[E comparable](s *Set[E]) {
+	for v := range s.All() {
+		time.Sleep(100 * time.Second)
+		fmt.Println(v)
+	}
+}