Added check for -lmmap for OS/2.

diff --git a/include/config.h.in b/include/config.h.in
index 3a2d167..2a5a5c3 100644
--- a/include/config.h.in
+++ b/include/config.h.in
@@ -279,6 +279,9 @@
 /* Define if you have the i386 library (-li386).  */
 #undef HAVE_LIBI386
 
+/* Define if you have the mmap library (-lmmap).  */
+#undef HAVE_LIBMMAP
+
 /* Define if you have the ncurses library (-lncurses).  */
 #undef HAVE_LIBNCURSES