Make use of C++14 make_index_sequence

[pippijn]

Change
https://github.com/Antique-team/clangml/blob/master/tools/bridgen/c%2B%2B/ocaml%2B%2B.h#L486
to use std::make_index_sequence
http://en.cppreference.com/w/cpp/utility/integer_sequence

[pippijn]

Actually, use std::index_sequence_for, instead.

[UnixJunkie]

Would it fix something?
This is C++14 and we are currently using c++11.

[UnixJunkie]

Even with -std=c++1y and clang++ 3.4, it doesn't compile:

tools/bridgen/c++/ocaml++.h:486:22: error: no member named 'index_sequence_for' in namespace 'std'

[pippijn]

It would fix nothing, but it would make the code clearer. Consider this low priority and something that can be done after C++14 is out.
Another example is using enable_if_t here:
https://github.com/Antique-team/clangml/blob/master/tools/bridgen/c%2B%2B/ocaml%2B%2B.h#L278