[libcxx] Revert set of atomic patches that broke lldb.

Revert "[libc++] Fix <atomic> failures on GCC"
Revert "[libc++] Change memory_order to an enum class"
Revert "[libc++] decoupling Freestanding atomic<T> from libatomic.a"

The lldb formatter nededs to be updated. Shafik and Louis will
coordinate to do so.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@355417 91177308-0d34-0410-b5e6-96231b3b80d8
6 files changed