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_mvc.mak b/src/Make_mvc.mak
index 52deb54..c948f37 100644
--- a/src/Make_mvc.mak
+++ b/src/Make_mvc.mak
@@ -721,6 +721,7 @@
 	$(OUTDIR)\ex_getln.obj \
 	$(OUTDIR)\farsi.obj \
 	$(OUTDIR)\fileio.obj \
+	$(OUTDIR)\findfile.obj \
 	$(OUTDIR)\fold.obj \
 	$(OUTDIR)\getchar.obj \
 	$(OUTDIR)\hardcopy.obj \
@@ -1407,6 +1408,8 @@
 
 $(OUTDIR)/fileio.obj:	$(OUTDIR) fileio.c  $(INCL)
 
+$(OUTDIR)/findfile.obj:	$(OUTDIR) findfile.c  $(INCL)
+
 $(OUTDIR)/fold.obj:	$(OUTDIR) fold.c  $(INCL)
 
 $(OUTDIR)/getchar.obj:	$(OUTDIR) getchar.c  $(INCL)
@@ -1645,6 +1648,7 @@
 	proto/ex_getln.pro \
 	proto/farsi.pro \
 	proto/fileio.pro \
+	proto/findfile.pro \
 	proto/getchar.pro \
 	proto/hardcopy.pro \
 	proto/hashtab.pro \