patch 8.1.0914: code related to findfile() is spread out

Problem:    Code related to findfile() is spread out.
Solution:   Put findfile() related code into a new source file. (Yegappan
            Lakshmanan, closes #3934)
diff --git a/src/Make_morph.mak b/src/Make_morph.mak
index 6bcae1a..a6e0dae 100644
--- a/src/Make_morph.mak
+++ b/src/Make_morph.mak
@@ -44,6 +44,7 @@
 	ex_getln.c						\
 	farsi.c							\
 	fileio.c						\
+	findfile.c						\
 	fold.c							\
 	getchar.c						\
 	hardcopy.c						\