Use the latest BDWGC code

Josh Peterson · Josh Peterson · commit 045076f3bfa1 · 2018-09-20T12:40:11.000-04:00
diff --git a/external/bdwgc b/external/bdwgc
@@ -1 +1 @@
-Subproject commit 395d3e4b972d7b6f80d10325dfd5267ecd6208eb
+Subproject commit edd22913569d3f31a45229099ebea3b9162128d6
