- Remove macros, have self-contained static inline functions.
  gcc_builtins.h, generic-msvc.h, rwlock.h and solaris.h now
  contain the full details about each of our native atomics implementations.
- Remove nolock.h, move contents into my_atomics.h
- Remove MY_ATOMIC_MODE_DUMMY and MY_ATOMIC_MODE
- make_transparent_unions() not needed anymore
- 32 bit MSVC workaround not needed anymore
- workaround for VS earlier than 2010 not needed anymore