add missing libltdl support files

diff --git a/libltdl/config/ar-lib b/libltdl/config/ar-lib
new file mode 120000 (symlink)
index 0000000..b686f5c
--- /dev/null
+++ b/libltdl/config/ar-lib
@@ -0,0 +1 @@
+/usr/local/Cellar/automake/1.15/share/automake-1.15/ar-lib
\ No newline at end of file