As it's causing some bot failures (and per request from kbarton).
This reverts commit r358543/ab70da07286e618016e78247e4a24fcb84077fda.
llvm-svn: 358546
Instead of depending on implicit padding from the structure layout code,
use a packed struct and emit the padding explicitly.
Differential Revision: https://reviews.llvm.org/D49710
llvm-svn: 337961