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/config.h.in b/src/config.h.in
index 166724c..8354930 100644
--- a/src/config.h.in
+++ b/src/config.h.in
@@ -174,6 +174,7 @@
 #undef HAVE_GETTIMEOFDAY
 #undef HAVE_GETWD
 #undef HAVE_ICONV
+#undef HAVE_INET_NTOP
 #undef HAVE_LOCALTIME_R
 #undef HAVE_LSTAT
 #undef HAVE_MEMSET