af_alg: Pacify --enable-gcc-warnings Problem reported by Assaf Gordon in: https://lists.gnu.org/r/bug-gnulib/2018-05/msg00041.html * lib/af_alg.c (afalg_buffer): Move local decls to pacify gcc -Wjump-misses-init. * lib/sha512.c (shaxxx_stream): Now static.