Revert "[MS] Don't statically initialize dllimport member function pointers"

This reverts commit r306137. It has problems on code like this:

  struct __declspec(dllimport) Foo {
    int a;
    int get_a() { return a; }
  };
  template <int (Foo::*Getter)()> struct HasValue {
    int operator()(Foo *p) { return (p->*Getter)(); }
  };
  int main() {
    Foo f;
    f.a = 3;
    int x = HasValue<&Foo::get_a>()(&f);
  }

llvm-svn: 306175