Refactors CompileUnoptimizedCode to do all the finalization for both
inner and the outermost function after having prepared and executed their
compile jobs. This will enable the function to be split into an off-thread
phase and a finalization main thread phase.

BUG=v8:5203

Change-Id: I400933c27b7aa52f9a7318b721adecfc94c80981
Reviewed-on: https://chromium-review.googlesource.com/602236
Commit-Queue: Ross McIlroy <rmcilroy@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47199}