Enable AVX512 *epi64 variants by updating stdarch

diff --git a/library/stdarch b/library/stdarch
index 3c3664355ef46e788b53080e521d6542fbddfd84..777efaf5644706b36706a7a5c51edb63835e05ca 160000 (submodule)
--- a/library/stdarch
+++ b/library/stdarch
@@ -1 +1 @@
-Subproject commit 3c3664355ef46e788b53080e521d6542fbddfd84
+Subproject commit 777efaf5644706b36706a7a5c51edb63835e05ca