The disassembler expects the actual instruction area of a code object
(i.e. from InstructionStart() to the first embedded metadata section
such as the handler table) to contain only valid instructions.

This changes asm::DataAlign() to pad with 0xcc bytes, which are int3
instructions on x64 and ia32.

Bug: v8:8559
Change-Id: I8a0920a85d4de89194e5c8d3d1a541d8b36fef92
Reviewed-on: https://chromium-review.googlesource.com/c/1375652Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58207}