Document PR79806 as a non-bug

[Bernd Schmidt]

I suggest we apply the following and close the PR as INVALID (not a 
bug). Ok?

Bernd

Index: pr65693.c
===================================================================
--- pr65693.c   (revision 245685)
+++ pr65693.c   (working copy)
@@ -2,6 +2,11 @@
 /* { dg-do compile } */
 /* { dg-options "-O2" } */

+/* This test relies on -O2 to optimize away the division operation
+   that's expanded as part of the alloca.  With -O0, the explicit use
+   of edx causes a compilation failure, which is expected
+   behaviour.  */
+
 int a;

 void