Fix invalid usage of layout_descriptor() function on 32-bit arch's,
which doesn't perform necessary checks. Test failure is observed only on
mips32 big-endian, and on mips32 little-endian as an alignment issue,
but the problem appears to be generic for all 32-bit arch's.

TEST=test/mjsunit/es6/classes-subclass-builtins.js
BUG=

Review URL: https://codereview.chromium.org/1522203004

Cr-Commit-Position: refs/heads/master@{#32887}