Slightly simplify make logic


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@8211 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/Makefile.rules b/Makefile.rules
index f002d0a..45a25ed 100644
--- a/Makefile.rules
+++ b/Makefile.rules
@@ -843,9 +843,7 @@
 #
 ifneq ($(MAKECMDGOALS),clean)
 ifneq ($(MAKECMDGOALS),distclean)
-ifneq ($(SourceDepend),)
--include $(SourceDepend)
-endif
+-include /dev/null $(SourceDepend)
 endif
 endif