Adapt sources to configurable config.h name
diff --git a/library/ecp.c b/library/ecp.c
index 4823804..7e965d3 100644
--- a/library/ecp.c
+++ b/library/ecp.c
@@ -44,7 +44,11 @@
  *     <http://eprint.iacr.org/2004/342.pdf>
  */
 
+#if !defined(POLARSSL_CONFIG_FILE)
 #include "polarssl/config.h"
+#else
+#include POLARSSL_CONFIG_FILE
+#endif
 
 #if defined(POLARSSL_ECP_C)