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_cyg_ming.mak b/src/Make_cyg_ming.mak
index 1e26add..48ce397 100644
--- a/src/Make_cyg_ming.mak
+++ b/src/Make_cyg_ming.mak
@@ -716,6 +716,7 @@
 	$(OUTDIR)/ex_getln.o \
 	$(OUTDIR)/farsi.o \
 	$(OUTDIR)/fileio.o \
+	$(OUTDIR)/findfile.o \
 	$(OUTDIR)/fold.o \
 	$(OUTDIR)/getchar.o \
 	$(OUTDIR)/hardcopy.o \