Updates the Math submodule to 7d64047.

stan-buildbot · stan-buildbot · commit 891fde44fd87 · 2021-10-18T03:34:18.000-04:00
diff --git a/lib/stan_math b/lib/stan_math
@@ -1 +1 @@
-Subproject commit 18cbbdfb1b8fa08d7d4c0b3785c4032bb01ceb6a
+Subproject commit 7d64047c4320ddd0a8f37a3071f04d6dfc852374
