patch 9.0.1110: build fails on Mac OS X 10.4/10.5

Problem:    Build fails on Mac OS X 10.4/10.5 .
Solution:   Check if the dispatch/dispatch.h header exists. (Evan Miller,
            closes #11746)
diff --git a/src/config.h.in b/src/config.h.in
index b77418c..6cb43da 100644
--- a/src/config.h.in
+++ b/src/config.h.in
@@ -236,6 +236,7 @@
 
 /* Define if you have the header file: */
 #undef HAVE_DIRENT_H
+#undef HAVE_DISPATCH_DISPATCH_H
 #undef HAVE_ERRNO_H
 #undef HAVE_FCNTL_H
 #undef HAVE_FRAME_H