Libc++ provides static assertions to detect reference binding issues inside
tuple. This patch adds tests for those diagnostics.
It should be noted that these static assertions technically violate the
standard since it allows these illegal bindings to occur.
Also see https://llvm.org/bugs/show_bug.cgi?id=20855
git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@276078 91177308-0d34-0410-b5e6-96231b3b80d8
