crypto libraries: use stdalign

crypto libraries: use stdalign

* lib/md4.c, lib/md5.c, lib/sha1.c, lib/sha256.c, lib/sha512.c:
Include <stdalign.h> and <stdint.h>.  Do not include <stddef.h>.
Do not include <stdlib.h> twice, in md4.c.
(UNALIGNED_P): Simplify by using alignof.  Use uintptr_t, not size_t,
because we are accessing a pointer's bit-pattern, not a size.
* modules/crypto/gc-md4 (Depends-on): Add stdalign.
* modules/crypto/gc-md5, modules/crypto/gc-sha1, modules/crypto/md4:
* modules/crypto/md5, modules/crypto/sha1, modules/crypto/sha256:
* modules/crypto/sha512: Likewise.