This fixes the name stored with functions where the declaration was
hoisted above the actual function definition. It also extends test
coverage and emits proper source position mapping for such cases.

R=clemensh@chromium.org
TEST=mjsunit/wasm/asm-wasm-stack
BUG=v8:6127

Change-Id: I675a98b244fe2157925e799b5c46b7f6bd53c9da
Reviewed-on: https://chromium-review.googlesource.com/466247Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#44361}