[libc++] Fixes operator& hijacking atomic types.

This uses std::addressof everywherein atomic. This is not strictly
needed for the integral and floating point specializations. They should
not be used by user defined types. But it's easier to fix everything.

Note these changes are made using a WIP clang-tidy plugin.

Reviewed By: #libc, ldionne

Differential Revision: https://reviews.llvm.org/D144786