Type check bounds expression arguments

[secure-sw-dev-bot]

This issue was copied from checkedc/checkedc-clang#45

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This change adds type checking for bounds expressions of the form (bounds(e1, e2). The type checking rules are:

• The types of e1 and e2 must both be pointer types.
• The types e1 and e2 must both be pointers to objects or incomplete types, and
• The types of e1 and e2 must both be pointers to the same type or one of them must be a pointer to void.

Testing:

• New tests will be added to typechecking\bounds.c in the Checked C GitHub repo. These will be committed separately.
• Passes existing clang tests.

[secure-sw-dev-bot]

Comment from @awruef:

Left two comments, otherwise looks fine to me.

[secure-sw-dev-bot]

Comment from @reubeno:

Ditto. Left a few questions, otherwise looks good.

[secure-sw-dev-bot]

Comment from @dtarditi:

I've address the code review feedback and improved commenting. I also answered the questions above. I'll commit this now. If you want additional changes, let me know.