Another bug :(

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@66708 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/tools/Makefile b/tools/Makefile
index e7b21ab..756d7d5 100644
--- a/tools/Makefile
+++ b/tools/Makefile
@@ -33,7 +33,7 @@
 
 # No support for lto / gold on windows targets
 ifeq ($(OS), $(filter $(OS), Cygwin MingW))
-  DIRS = $(filter-out lto gold, $(DIRS))
+  DIRS := $(filter-out lto gold, $(DIRS))
 endif
 
 include $(LEVEL)/Makefile.common