upgrade stdsimd to branch with breaking change for crater run

gnzlbg · gnzlbg · commit 469726187e57 · 2018-11-03T17:36:08.000+01:00
diff --git a/src/stdsimd b/src/stdsimd
@@ -1 +1 @@
-Subproject commit 431766a3fbcfb6dafb2d5a3866c1609bf44ee554
+Subproject commit 12e8ab4a0d0344f851f79862cd2e288dae318be6
