formula: fix build, undef Idle

Change-Id: If256bba5d8207a955c06713db7141831b53324c7
diff --git a/include/formula/funcutl.hxx b/include/formula/funcutl.hxx
index f0ea363..e6d03bed 100644
--- a/include/formula/funcutl.hxx
+++ b/include/formula/funcutl.hxx
@@ -23,6 +23,7 @@
#include <vcl/fixed.hxx>
#include <vcl/button.hxx>
#include <vcl/edit.hxx>
#include <vcl/idle.hxx>
#include <formula/formuladllapi.h>

namespace formula {