Fix error recovery with in-class initializer.

Previously, for a field with an invalid in-class initializer, we
would create a CXXDefaultInitExpr referring to a null Expr*.
This is not a good idea.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@185216 91177308-0d34-0410-b5e6-96231b3b80d8
PR7927, PR16247: Reimplement handling of matching extern "C" declarations
across scopes.

When we declare an extern "C" name that is not a redeclaration of an entity in
the same scope, check whether it redeclares some extern "C" entity from another
scope, and if not, check whether it conflicts with a (non-extern-"C") entity in
the translation unit.

When we declare a name in the translation unit that is not a redeclaration,
check whether it conflicts with any extern "C" entities (possibly from other
scopes).


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@185229 91177308-0d34-0410-b5e6-96231b3b80d8
Remove dead code.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@185231 91177308-0d34-0410-b5e6-96231b3b80d8