[turbofan] Fix JSInliner to handle non-returning bodies.

[turbofan] Fix JSInliner to handle non-returning bodies.

The assumption that every function body produces a value does not hold
for functions that e.g. unconditionally throw or endlessly loop. This
fixes the inlining logic to handle such cases.

R=bmeurer@chromium.org
TEST=mjsunit/regress/regress-crbug-530598
BUG=chromium:530598
LOG=n

Review URL: https://codereview.chromium.org/1333193005

Cr-Commit-Position: refs/heads/master@{#30738}