Fix various build failures on Windows (Courtesy of rockerinthelocker)

lib/isc/win32/include/isc/platform.h.in

@@ -36,9 +36,6 @@
 #define ISC_PLATFORM_NEEDNTOP
 #define ISC_PLATFORM_NEEDPTON
 #define ISC_PLATFORM_HAVESOCKADDRSTORAGE
-#if _MSC_VER >= 1900
-#define ISC_PLATFORM_HAVETFO
-#endif
 
 #define ISC_PLATFORM_NEEDSTRSEP
 #define ISC_PLATFORM_NEEDSTRLCPY

win32utils/Configure

@@ -1153,6 +1153,11 @@ if ($vcredist_path eq " --infer-- ") {
                                            "redist", "1033"));
     }
 
+    # 'VCToolsRedistDir' is available since Visual Studio 2017.
+    if ($ENV{"VCToolsRedistDir"}) {
+        push(@vcpaths, $ENV{"VCToolsRedistDir"});
+    }
+
     my $rfile;
     if ($want_win32 eq "yes") {
         $rfile = "vcredist_x86.exe";