patch 8.2.0903: comparing WINVER does not work correctly

Problem:    comparing WINVER does not work correctly.
Solution:   Use arithmethic expansion. (Ozaki Kiichi, closes #6197)
diff --git a/src/Make_cyg_ming.mak b/src/Make_cyg_ming.mak
index 39f1e84..890c956 100644
--- a/src/Make_cyg_ming.mak
+++ b/src/Make_cyg_ming.mak
@@ -625,7 +625,7 @@
 
 ifeq ($(CHANNEL),yes)
 DEFINES += -DFEAT_JOB_CHANNEL -DFEAT_IPV6
- ifeq ($(shell expr "$(WINVER)" \>= 0x600),1)
+ ifeq ($(shell expr "$$(($(WINVER)))" \>= "$$((0x600))"),1)
 DEFINES += -DHAVE_INET_NTOP
  endif
 endif