* lib/sha256.c (set_uint32): New function.
(sha256_read_ctx, sha224_read_ctx): Use it.
* lib/sha512.c (set_uint64): New function.
(sha512_read_ctx, sha384_read_ctx): Use it.
* lib/sha256.h: Remove warning about alignment constraint.
* lib/sha512.h: Likewise.
Prompted by similar changes in gnulib's sha1 and md[45] modules.