Implement template instantiation for static data members of class

Implement template instantiation for static data members of class
templates, including in-class initializers. For example:

  template<typename T, T Divisor>
  class X {
  public:
    static const T value = 10 / Divisor;
  };

instantiated with, e.g.,

  X<int, 5>::value

to get the value '2'.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@67715 91177308-0d34-0410-b5e6-96231b3b80d8