[NFC][libcxx] Mark P1006 as implemented in LLVM 8.0

It was implemented in https://reviews.llvm.org/D53867

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@346765 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed