This fixes cases where the omission of return type annotation of calls
to stdlib function was rejected, because a surrounding {fround} call
used to be misinterpreted as an annotation instead of a rounding.

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

Change-Id: Idec0ef1740ebf8eda969ff05dd1c90252de87a6b
Reviewed-on: https://chromium-review.googlesource.com/493349
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45057}