Padding of enums required to avoid LLVM assert

[nikomatsakis]

For some reason, when changing the size of the expr_ enum in libsyntax, we triggered an LLVM assertion that the size must be a multiple of 64 bytes.

Some discussion of possible causes from IRC:

[16:30:46] <@pcwalton> possibly an LLVM optimizer pass is turning a packed struct into a large i1234567 and causing the asm printer to blow up
[16:30:56] <@pcwalton> I would think selection DAG would legalize it away but maybe not
[16:33:32] <echristo> pcwalton: it could be sroa as well.
[16:33:42] <@pcwalton> yeah
[16:34:01] <echristo> (which has been rewritten somewhat recently and so might be worth moving forward if you aren't there. if you are it might be worth tracking down)

[sanxiyn]

I can't find the workaround in the source. Is this not a problem any more?

[nikomatsakis]

It has quite possibly been fixed, I am not sure. We should probably just close until we see again, since there is no easy way to reproduce.