instead or additionally to string.h, in preparation for functions move.
* moves str[n]casecmp() functions and others to strings.h.
* strings.h doesn't include string.h anymore.
* this solves #10949
* No need for the atomically changed variables to be declared as
volatile.
* Drop support for atomically getting and setting unaligned data.
* Introduce atomic_get_and_set[64]() which works the same as
atomic_set[64]() used to. atomic_set[64]() does not return the
previous value anymore.
Jérôme Duval