update compiler-rt with iOS linking warnings workaround

TimNN · TimNN · commit 56ceef2ebe8f · 2016-07-04T19:11:03.000+02:00
closes rust-lang#34617.
diff --git a/src/compiler-rt b/src/compiler-rt
@@ -1 +1 @@
-Subproject commit a1ef94b76029780a510bc2dc9c6a791bd091ff19
+Subproject commit ac3d1cda612edccb6f1da53cbf7716e248405f3b
