patch 8.2.0594: MS-Windows: cannot build with WINVER set to 0x0501

Problem:    MS-Windows: cannot build with WINVER set to 0x0501.
Solution:   Only use inet_ntop() when available. (Ozaki Kiichi, closes #5946)
diff --git a/src/Make_mvc.mak b/src/Make_mvc.mak
index e95a94a..ebc059f 100644
--- a/src/Make_mvc.mak
+++ b/src/Make_mvc.mak
@@ -317,6 +317,10 @@
 CPU = ix86
 !endif
 
+### Set the default $(WINVER) to make it work with VC++7.0 (VS.NET)
+!ifndef WINVER
+WINVER = 0x0501
+!endif
 
 # Flag to turn on Win64 compatibility warnings for VC7.x and VC8.
 WP64CHECK = /Wp64
@@ -468,6 +472,9 @@
 CHANNEL_PRO	= proto/channel.pro
 CHANNEL_OBJ	= $(OBJDIR)/channel.obj
 CHANNEL_DEFS	= -DFEAT_JOB_CHANNEL -DFEAT_IPV6
+! if $(WINVER) >= 0x600
+CHANNEL_DEFS	= $(CHANNEL_DEFS) -DHAVE_INET_NTOP
+! endif
 
 NETBEANS_LIB	= WSock32.lib Ws2_32.lib
 !endif
@@ -493,11 +500,6 @@
 CON_LIB = $(CON_LIB) /DELAYLOAD:comdlg32.dll /DELAYLOAD:ole32.dll DelayImp.lib
 !endif
 
-### Set the default $(WINVER) to make it work with VC++7.0 (VS.NET)
-!ifndef WINVER
-WINVER = 0x0501
-!endif
-
 # If you have a fixed directory for $VIM or $VIMRUNTIME, other than the normal
 # default, use these lines.
 #VIMRCLOC = somewhere