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_ivc.mak b/src/Make_ivc.mak
index 96d6a47..a02ba96 100644
--- a/src/Make_ivc.mak
+++ b/src/Make_ivc.mak
@@ -230,6 +230,7 @@
 	"$(INTDIR)/ex_getln.obj" \
 	"$(INTDIR)/farsi.obj" \
 	"$(INTDIR)/fileio.obj" \
+	"$(INTDIR)/findfile.obj" \
 	"$(INTDIR)/fold.obj" \
 	"$(INTDIR)/getchar.obj" \
 	"$(INTDIR)/hardcopy.obj" \
@@ -419,6 +420,10 @@
 SOURCE=.\fileio.c
 # End Source File
 # Begin Source File
+#
+SOURCE=.\findfile.c
+# End Source File
+# Begin Source File
 
 SOURCE=.\fold.c
 # End Source File