build BUGFIX vdprintf() detection
diff --git a/src/config.h.in b/src/config.h.in
index be52bdb..a65de05 100644
--- a/src/config.h.in
+++ b/src/config.h.in
@@ -17,6 +17,8 @@
 
 #cmakedefine APPLE
 
+#cmakedefine HAVE_VDPRINTF
+
 /**
  * @brief Compiler flag for unused function attributes
  */