Revert r220153: "CodeGen: ConstStructBuilder must verify packed constraints after padding"

This commit caused two tests in LNT to regress. I'm able to reproduce on
any platform and will send reproduction steps to the original commit
log. This should restore the LNT bots that have been failing.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@220169 91177308-0d34-0410-b5e6-96231b3b80d8