patch 7.4.996

Problem:    New GDK files and testdir/Make_all.mak missing from distribution.
            PC build instructions are outdated.
Solution:   Add the file to the list.  Update PC build instructions.

src/version.c

@@ -741,6 +741,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    996,
 /**/
     995,
 /**/