Include configuration file for all headers

Include the configuration file for all headers that were not
included.
diff --git a/include/mbedtls/error.h b/include/mbedtls/error.h
index 8b4d3a8..ef22bc6 100644
--- a/include/mbedtls/error.h
+++ b/include/mbedtls/error.h
@@ -24,6 +24,12 @@
 #ifndef MBEDTLS_ERROR_H
 #define MBEDTLS_ERROR_H
 
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
+
 #include <stddef.h>
 
 /**