Wording tweak from Dan.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@107343 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/www/compatibility.html b/www/compatibility.html
index fb47400..8a2f05b 100644
--- a/www/compatibility.html
+++ b/www/compatibility.html
@@ -114,7 +114,7 @@
 <h3 id="lvalue-cast">Lvalue casts</h3>
 <!-- ======================================================================= -->
 
-<p>GCC permits casting the left-hand side of an assignment to a
+<p>Old versions of GCC permit casting the left-hand side of an assignment to a
 different type. Clang produces an error on similar code, e.g.,</p>
 
 <pre>