Add a compatibility function attribute (and flag) for nacl-gcc to

gcc/function.c

Index: gcc/function.c
diff --git a/gcc/function.c b/gcc/function.c
index d582fea6e6539ff774d7463cd546d2163410a75f..035c056a8ed4b568f72017aa27a5661679f3f790 100644
--- a/gcc/function.c
+++ b/gcc/function.c
@@ -1826,6 +1826,30 @@ struct rtl_opt_pass pass_instantiate_virtual_regs =
  }
 };
 
+/* HACK: If |maybe_call| is a call expression, grab additional type attributes
+ * from the expression (e.g., from a function pointer type) which may not
+ * have been present in a function decl. This must NOT affect the original
+ * function type/decl, so make a copy if it really changed.
+ * We may be able to narrow this hack to just propagate the "pnaclcall"
+ * attribute...
+ */
+static tree copy_attributes_if_call (const_tree maybe_call, const_tree fntype) {
+  if (TREE_CODE (maybe_call) == CALL_EXPR) {
+    tree new_attributes =
+        merge_type_attributes(fntype,
+                              TREE_TYPE (TREE_TYPE (
+                                  CALL_EXPR_FN (maybe_call))));
+    if (!attribute_list_equal (TYPE_ATTRIBUTES (fntype),
+                               new_attributes)) {
+      tree new_fntype = copy_node (fntype);
+      TYPE_ATTRIBUTES (new_fntype) = new_attributes;
+      return new_fntype;
+    }
+    return fntype;
+  }
+  return fntype;
+}
+
 
 /* Return 1 if EXP is an aggregate type (or a value with aggregate type).
    This means a type for which function calls must pass an address to the
@@ -1853,10 +1877,14 @@ aggregate_value_p (const_tree exp, const_tree fntype)
 	fntype = (fndecl
 		  ? TREE_TYPE (fndecl)
 		  : TREE_TYPE (TREE_TYPE (CALL_EXPR_FN (fntype))));
+    /* HACK to grab attributes from the callexp type as well as the decl. */
+	fntype = copy_attributes_if_call (exp, fntype);
 	break;
       case FUNCTION_DECL:
 	fndecl = fntype;
 	fntype = TREE_TYPE (fndecl);
+    /* HACK to grab attributes from the callexp type as well as the decl. */
+	fntype = copy_attributes_if_call (exp, fntype);
 	break;
       case FUNCTION_TYPE:
       case METHOD_TYPE: