When we attempt to create a temporary object of class type, be sure

When we attempt to create a temporary object of class type, be sure
that the type we're copying is complete.

Boost.Regex now builds, although it's failing its regression tests
with our favorite "Sema doesn't consider destructor as used."
assertion.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@102271 91177308-0d34-0410-b5e6-96231b3b80d8