Make size_of, align_of, and element_offset functions return u64 instead of uint in trans::machine

[nathanielherman]

For #5172

[alexcrichton]

This looks a little suspicious, I don't think that we want to change a target's call to memcpy, we only want to change the compiler's representation of offsets and sizes to u64 to accommodate when a 32-bit platform cross-compiles to a 64-bit platform.

[alexcrichton]

cc @jld, I have some comments, but I'm unfamiliar with this code enough to know whether this is all of the places which need to get changed.

[nathanielherman]

Ah so C_* represents values in the code the compiler produces (target)? That makes sense.

Though, how could I safely create a C_uint for a 64-bit platform when compiled on a 32-bit platform? Wouldn't C_uint(cx, someU64 as uint) downcast to u32 if cross-compiled on a 32-bit platform, for a 64-bit platform?

[alexcrichton]

A 32-bit platform cannot create any structs or have any offsets larger than 32-bits, so downcasting should always be fine.

[nathanielherman]

OK I've updated it so that there shouldn't be anymore target code using C_u64's.

[alexcrichton]

This looks good to me!

Could you rebase the commits into one commit?

[nathanielherman]

Yup should be good now.