patch 8.2.4686: configure doesn't find the Motif library with Cygwin

Problem:    Configure doesn't find the Motif library with Cygwin.
Solution:   Check for libXm.dll.a. (Kelvin Lee, closes #10077)
diff --git a/src/version.c b/src/version.c
index 930f92e..fffd85f 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    4686,
+/**/
     4685,
 /**/
     4684,