Merging r310905 and r310994:

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r310905 | rnk | 2017-08-14 18:17:47 -0700 (Mon, 14 Aug 2017) | 11 lines

Avoid PointerIntPair of constexpr EvalInfo structs

They are stack allocated, so their alignment is not to be trusted.
32-bit MSVC only guarantees 4 byte stack alignment, even though alignof
would tell you otherwise. I tried fixing this with __declspec align, but
that apparently upsets GCC. Hopefully this version will satisfy all
compilers.

See PR32018 for some info about the mingw issues.

Should supercede https://reviews.llvm.org/D34873
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r310994 | chandlerc | 2017-08-16 00:22:49 -0700 (Wed, 16 Aug 2017) | 6 lines

Fix a UBSan failure where this boolean was copied when uninitialized.

When r310905 moved the pointer and bool out of a PointerIntPair, it made
them end up uninitialized and caused UBSan failures when copying the
uninitialized boolean. However, making the pointer be null should avoid
the reference to the boolean entirely.
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llvm-svn: 318225