During the review of #203680 I noticed that Mach-O objcopy files seems
to use `alignTo` and import `Alignment.h` to align some offsets to page
boundaries and similar requirements. However, the `alignTo` in
`Alignment.h`, while being intended for powers of 2, requires using an
alignment of type `llvm::Align`, and needs explicit conversion from
`uint64_t` and similar. Single `Alignment.h` includes `MathExtras.h`,
the `alignTo` being invoked ends up being a generic `alignTo` that does
not require powers of 2, and perform divisions and multiplications.
While some of those might be optimized by the compiler into efficient
power of 2 operations, there's an explicit `alignToPowerOf2` version
that is optimized and asserts the alignment is a power of 2 (with
asserts enabled). Since all the alignments should be power of 2 for the
Mach-O binary format, change from `alignTo` to `alignToPowerOf2` to make
the fact more visible (and get the extra safety net of the assertions).
As expected, the test suite of objcopy doesn't show any regressions, but
I have not done a performance benchmark around this either.
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