Add libipt as a submodule of dynamorio

[dolanzhao]

Adding submodules in general brings up a bunch of auxiliary support we probably want. I wonder if we should separate this out as its own PR. I assume we want the submodule to be initialized all the time? If so, things we would want:

• We have to tell GA CI to init submodules: submodules: true arg to checkout step
• Add submodule update to make/git/devsetup.sh
• Add submodule update to make/git/git_pullall.sh
• Potentially add to how-to-build docs if not completely automated
• Potentially add a pre-commit hook to prevent the common mistake of accidentally rolling back a recent submodule update when switching branches

Originally posted by @derekbruening in #5515 (comment)

[derekbruening]

Not sure this needed to be its own issue? The reason libipt is desired is for dr$sim kernel traces #5505.