patch 8.2.1597: the channel source file is too big

Problem:    The channel source file is too big.
Solution:   Move job related code to a new source file.
diff --git a/src/Make_cyg_ming.mak b/src/Make_cyg_ming.mak
index 5fc0833..75021cc 100644
--- a/src/Make_cyg_ming.mak
+++ b/src/Make_cyg_ming.mak
@@ -870,7 +870,7 @@
 endif
 
 ifeq ($(CHANNEL),yes)
-OBJ += $(OUTDIR)/channel.o
+OBJ += $(OUTDIR)/job.o $(OUTDIR)/channel.o
 LIB += -lwsock32 -lws2_32
 endif