Undisable a test for a c++98-compat warning for inheriting constructors now that we implement them.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@186768 91177308-0d34-0410-b5e6-96231b3b80d8
Add missing check for creating an instance of an abstract class through an
implicit conversion sequence.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@186769 91177308-0d34-0410-b5e6-96231b3b80d8