Now that we have declared/defined tag types within DeclGroups,

instantiation of tags local to member functions of class templates
(and, eventually, function templates) works when the tag is defined as
part of the decl-specifier-seq, e.g.,

  struct S { T x, y; } s1;

Also, make sure that we don't try to default-initialize a dependent
type.

llvm-svn: 72568