Allow the Makefile build system to find the extra repo if it is checked
out.

Unfortunately, the existing makefiles for the extra repo don't specify
the correct library dependencies. Fixing that next. If you're following
along, you'll get linker errors.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@161549 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/tools/Makefile b/tools/Makefile
index 5059ade..dad767c 100644
--- a/tools/Makefile
+++ b/tools/Makefile
@@ -8,8 +8,9 @@
 ##===----------------------------------------------------------------------===##
 
 CLANG_LEVEL := ..
+
 DIRS := driver libclang c-index-test arcmt-test c-arcmt-test diagtool \
-        clang-check
+        clang-check $(patsubst %/Makefile,%,$(wildcard extra/Makefile))
 
 include $(CLANG_LEVEL)/../../Makefile.config