[dia] [clang-cl] Avoid l-value cast for everything but msvc

[Hans Breuer <hans src gnome org>]

commit 1c8b01f527b5356d120c042e8546976fcde9f8f4
Author: Hans Breuer <hans breuer org>
Date:   Sat Dec 14 12:43:08 2013 +0100

    [clang-cl] Avoid l-value cast for everything but msvc
    
    clang-cl did not like that pattern as well even in compatibility mode

 app/diagram_tree_model.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/app/diagram_tree_model.c b/app/diagram_tree_model.c
index 59c1781..2b5078e 100644
--- a/app/diagram_tree_model.c
+++ b/app/diagram_tree_model.c
@@ -32,7 +32,7 @@
 #include "diagram_tree_model.h"
 
 /* accessing iter fileds by name by */
-#ifdef _MSC_VER
+#if defined(_MSC_VER) && !defined(__clang__)
 /* GCC does not like the pattern */
 /* error: lvalue required as left operand of assignment */
 #define NODE_DIAGRAM(it) ((DiagramData*)(it->user_data))