This patch reverts the changes to tuple which fixed construction from
types derived from tuple. It breaks the code mentioned in llvm.org/PR31384.
I'll follow this commit up with a test case.
git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@289773 91177308-0d34-0410-b5e6-96231b3b80d8