A64: Fixes for the veneers emission.

A64: Fixes for the veneers emission.

This patch includes 3 fixes for veneers emission.

1) Block veneer pools emission in the PatchingAssembler.
2) Fix the check for veneer pool emission just before a constant pool.
3) Forbid copy of labels. The list of JumpTableEntry used to track the
   deoptimization table entries would make copies of the labels when growing.
   Doing so, it would confuse the Assembler that was tracking the labels via
   pointers.

R=ulan@chromium.org

Committed: https://code.google.com/p/v8/source/detail?r=19941

[ulan, 2014-03-14 10:26:36]

lgtm

[Alexandre Rames, 2014-03-14 15:14:52]

Committed patchset #1 manually as r19941 (presubmit successful).