More libc++ warning suppression on Linux; no functionality change

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@174636 91177308-0d34-0410-b5e6-96231b3b80d8
Another libc++ warning suppression on Linux; no functionality change

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@174637 91177308-0d34-0410-b5e6-96231b3b80d8