tuple was accidentally lacking a valid copy assignment operator.  It went undetected because I had failed to test assigning from a const lvalue.  This fixes http://llvm.org/bugs/show_bug.cgi?id=11921

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@150613 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed