Adapt sources to configurable config.h name
diff --git a/library/sha1.c b/library/sha1.c
index f02d6e6..b89db32 100644
--- a/library/sha1.c
+++ b/library/sha1.c
@@ -28,7 +28,11 @@
  *  http://www.itl.nist.gov/fipspubs/fip180-1.htm
  */
 
+#if !defined(POLARSSL_CONFIG_FILE)
 #include "polarssl/config.h"
+#else
+#include POLARSSL_CONFIG_FILE
+#endif
 
 #if defined(POLARSSL_SHA1_C)