[PATCH] Introduce llvm/ADT/OptionSet.h utility class

[Argyrios Kyrtzidis via llvm-commits]

I’ve took the liberty of committing in r260652, since this is general goodness and doesn’t affect existing code.

> On Feb 10, 2016, at 9:23 PM, Argyrios Kyrtzidis <kyrtzidis at apple.com> wrote:
> 
> Hi all,
> 
> The attached patch introduces ‘OptionSet’ in llvm/ADT headers, which is a utility class that makes it convenient to work with enumerators representing bit options.
> 
> We have found it useful in the swift repo (https://github.com/apple/swift/blob/master/include/swift/Basic/OptionSet.h) and I think it will be useful to other llvm projects as well.
> 
> Let me know if you think it is ok to commit in llvm repo.
> 
> <optionset.patch>