Classes inside lambdas are local not nested.

If a lambda used as default argument in a method declaration contained
a local class, that class was incorrectly recognized as nested class.
In this case compiler tried to postpone parsing of this class until
the enclosing class is finished, which caused crashes in some cases.

This change fixes PR13987.

Differential Revision: http://reviews.llvm.org/D11006

llvm-svn: 242132