[turbofan] Use "leal" in even more situations

Achieve more than parity with modes currently handled on ia32 in preparation for
porting the entire mechanism to ia32, including supporting mul of constants 3,
5 and 9 with "leal" instructions.

TEST=unittests

Review URL: https://codereview.chromium.org/774193003

Cr-Commit-Position: refs/heads/master@{#25677}
Finally drop outdated misleading runtime.js comment.

R=bmeurer@chromium.org

Review URL: https://codereview.chromium.org/765833004

Cr-Commit-Position: refs/heads/master@{#25678}
When generating code for ia32, make sure that there is enough reloc space

Compare with LCodeGen::FinishCode

BUG=none
R=jarin@chromium.org,mstarzinger@chromium.org
LOG=n

Review URL: https://codereview.chromium.org/777243002

Cr-Commit-Position: refs/heads/master@{#25679}