Try harder to evaluate expressions when printing assembly.

When printing assembly we don't have a Layout object, but we can still
try to fold some constants.

Testcase by Ulrich Weigand.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@203677 91177308-0d34-0410-b5e6-96231b3b80d8
Correct typo ("a entry" -> "an entry")

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@203678 91177308-0d34-0410-b5e6-96231b3b80d8