Correct the grammar for __builtin_astype.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@143777 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Parse/ParseExpr.cpp b/lib/Parse/ParseExpr.cpp
index 4f45114..f77d8ea 100644
--- a/lib/Parse/ParseExpr.cpp
+++ b/lib/Parse/ParseExpr.cpp
@@ -1582,7 +1582,7 @@
 /// [GNU]   '__builtin_choose_expr' '(' assign-expr ',' assign-expr ','
 ///                                     assign-expr ')'
 /// [GNU]   '__builtin_types_compatible_p' '(' type-name ',' type-name ')'
-/// [OCL]   '__builtin_astype' '(' type-name expr ')'
+/// [OCL]   '__builtin_astype' '(' assignment-expression ',' type-name ')'
 ///
 /// [GNU] offsetof-member-designator:
 /// [GNU]   identifier