Assume __is_final,  __is_base_of, and friends.

All the compilers we support provide these builtins. We don't
need to do a configuration dance anymore.

This patch also cleans up some dead or almost dead
C++11 feature detection macros.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@364047 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed