BLAKE2S_IV4
BLAKE2S_IV1, BLAKE2S_IV2, BLAKE2S_IV3, BLAKE2S_IV4,
ctx->h[4] = BLAKE2S_IV4;
v[12] = BLAKE2S_IV4 ^ ctx->t[0];
v[12] = BLAKE2S_IV4 ^ ctx->t[0];
ctx->h[4] = BLAKE2S_IV4;