Log Message:
digest: fix aliasing bug with gcc 11

gcc 11 with -O2 optimizes away the store of the bit length into the
last 8 bytes of the context buffer due to an aliasing violation
(stored through uint64_t, retrieved through uint32_t).

To fix this, import the NetBSD patch from christos[0] which makes
it use memcpy instead.

[0] \ 
http://cvsweb.netbsd.org/bsdweb.cgi/src/common/lib/libc/hash/sha2/sha2.c.diff?r1=1.12&r2=1.13