patch 9.0.0526: MS-Windows: still some support for XP and old compilers

Problem:    MS-Windows: still some support for XP and old compilers.
Solution:   Remove XP support and mention of old compilers. (Ken Takata,
            closes #11183)
diff --git a/src/version.c b/src/version.c
index bdeb67e..76955bb 100644
--- a/src/version.c
+++ b/src/version.c
@@ -700,6 +700,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    526,
+/**/
     525,
 /**/
     524,