Don't assert on initialized typedef declarations in classes:

  struct {
    typedef int A = 0;
  };

According to the C++11 standard, this is not ill-formed, but does not have any ascribed meaning. We can't reasonably accept it, so treat it as ill-formed.

Also switch C++ from an incorrect 'fields can only be initialized in constructors' diagnostic for this case to C's 'illegal initializer (only variables can be initialized)'

llvm-svn: 132890