patch 8.0.0881: win32.mak no longer included in Windows SDK

Problem:    win32.mak no longer included in Windows SDK.
Solution:   Do not include win32.mak. (Ken Takata)
diff --git a/src/version.c b/src/version.c
index 19e2a0d..2b489ff 100644
--- a/src/version.c
+++ b/src/version.c
@@ -770,6 +770,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    881,
+/**/
     880,
 /**/
     879,