We may not emit bytecode for the evaluation of the to-be-returned
expression. In that case we cannot set two return positions for a return
statement (one before and one after the expression evaluation). This
sets the interpreter apart from full-codegen.

Make sure that we always have the second of the two return positions.

Note that we end up with separate test cases for ignition and FCG.

R=rmcilroy@chromium.org, vogelheim@chromium.org
BUG=v8:4690
LOG=N

Review URL: https://codereview.chromium.org/1801473003

Cr-Commit-Position: refs/heads/master@{#34771}