Remove obsolete CXX11 buld instructions

There's an element of guesswork involved in the GCC updates but it seems better
than what was there before.

git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@207912 91177308-0d34-0410-b5e6-96231b3b80d8
Track recent changes in clang internals

git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@207913 91177308-0d34-0410-b5e6-96231b3b80d8