fix rdar://8360877 a really nasty miscompilation in Boost.Xpressive

fix rdar://8360877 a really nasty miscompilation in Boost.Xpressive
caused by my ABI work.  Passing:

struct outer {
  int x;
  struct epsilon_matcher {} e;
  int f;
};

as {i32,i32} isn't safe, because the offset of the second element
needs to be at 8 when it is interpreted as a memory value.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@112686 91177308-0d34-0410-b5e6-96231b3b80d8