Sema::RequireCompleteType currently attempts to

Sema::RequireCompleteType currently attempts to
instantiate a class from its template pattern
before it consults the ExternalASTSource.  LLDB
in particular will sometimes provide patterns
that need to be completed first.

To make this possible, I have moved the
completion before the code that does the
instantiation, allowing the ExternalASTSource
to provide the required information.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@146715 91177308-0d34-0410-b5e6-96231b3b80d8