Change constant pool marker to be the unconditional, permanently undefined instruction.

Change constant pool marker to be the unconditional, permanently undefined instruction.

The previously-used instruction isn't guaranteed to always be undefined,
and the encoding used was conditional (failing the condition on an
undefined instruction is itself undefined and not guaranteed to
fault!). I would have like to use a more clever encoding (see bug 2963),
but we need the extra bits to encode the size of the constant pool.

BUG=security
R=ulan@chromium.org

Committed: https://code.google.com/p/v8/source/detail?r=12791

[ulan, 2012-10-22 14:31:34]

LGTM, I will land it for you.

[ulan, 2012-10-22 14:32:34]

[+v8-dev]