Switch clang to r353983

Bug: 126457671
Bug: 123638879
Bug: 128878287
Test: go/clang-r353983-testing
Change-Id: I7f16e68f0f521ff55587084932d175b704e452c9
diff --git a/cc/lto.go b/cc/lto.go
index 6302748..0d7a246 100644
--- a/cc/lto.go
+++ b/cc/lto.go
@@ -83,8 +83,7 @@
 	if lto.LTO() {
 		var ltoFlag string
 		if Bool(lto.Properties.Lto.Thin) {
-			ltoFlag = "-flto=thin"
-
+			ltoFlag = "-flto=thin -fsplit-lto-unit"
 		} else {
 			ltoFlag = "-flto"
 		}