patch 8.1.0408: MSVC: cannot use the "x64" native compiler option

Problem:    MSVC: cannot use the "x64" native compiler option.
Solution:   Ignore case for %Platform%.  Improve documentation. (Ken Takata)
diff --git a/src/version.c b/src/version.c
index 9f4a0ec..51601a0 100644
--- a/src/version.c
+++ b/src/version.c
@@ -795,6 +795,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    408,
+/**/
     407,
 /**/
     406,