Adapt sources to configurable config.h name
diff --git a/include/polarssl/entropy_poll.h b/include/polarssl/entropy_poll.h
index 0116598..92efa00 100644
--- a/include/polarssl/entropy_poll.h
+++ b/include/polarssl/entropy_poll.h
@@ -29,7 +29,11 @@
 
 #include <string.h>
 
+#if !defined(POLARSSL_CONFIG_FILE)
 #include "config.h"
+#else
+#include POLARSSL_CONFIG_FILE
+#endif
 
 #ifdef __cplusplus
 extern "C" {