[libcxx] Fix tuple construction/assignment from types derived from tuple/pair/array.

Summary:
The standard requires tuple have the following constructors:
```
tuple(tuple<OtherTypes...> const&);
tuple(tuple<OtherTypes...> &&);
tuple(pair<T1, T2> const&);
tuple(pair<T1, T2> &&);
tuple(array<T, N> const&);
tuple(array<T, N> &&);
```
However libc++ implements these as a single constructor with the signature:
```
template <class TupleLike, enable_if_t<__is_tuple_like<TupleLike>::value>>
tuple(TupleLike&&);
```

This causes the constructor to reject types derived from tuple-like types; Unlike if we had all of the concrete overloads, because they cause the derived->base conversion in the signature.

This patch fixes this issue by detecting derived types and the tuple-like base they are derived from. It does this by creating an overloaded function with signatures for each of tuple/pair/array and checking if the possibly derived type can convert to any of them.

This patch fixes [PR17550]( https://llvm.org/bugs/show_bug.cgi?id=17550)

This patch 

Reviewers: mclow.lists, K-ballo, mpark, EricWF

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D27606

llvm-svn: 289727

0 files changed, 0 insertions, 0 deletions