Sema: Warn on sizeof on binary ops on decayed arrays.

The array will decay into a pointer, creating an unexpected result.
sizeof(array + int) is an easy to make typo for sizeof(array) + int.

This was motivated by a NetBSD security bug, used sizeof(key - r) instead of
sizeof(key) - r, reducing entropy in a random number generator.
http://cvsweb.netbsd.org/bsdweb.cgi/src/sys/kern/subr_cprng.c.diff?r1=1.14&r2=1.15&only_with_tag=MAIN&f=h

Differential Revision: http://llvm-reviews.chandlerc.com/D571

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@178371 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/test/Sema/expr-comma.c b/test/Sema/expr-comma.c
index 7902715..e2beafe 100644
--- a/test/Sema/expr-comma.c
+++ b/test/Sema/expr-comma.c
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 %s -fsyntax-only -verify -std=c89
+// RUN: %clang_cc1 %s -fsyntax-only -verify -std=c89 -Wno-sizeof-array-decay
 // expected-no-diagnostics
 // rdar://6095180