Include configuration file to headers

Add inclusion to configration file in header files,
instead of relying on other header files to include
the configuration file. This issue resolves #1371
diff --git a/include/mbedtls/compat-1.3.h b/include/mbedtls/compat-1.3.h
index 213b691..a58b4724 100644
--- a/include/mbedtls/compat-1.3.h
+++ b/include/mbedtls/compat-1.3.h
@@ -25,6 +25,12 @@
  *  This file is part of mbed TLS (https://tls.mbed.org)
  */
 
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
+
 #if ! defined(MBEDTLS_DEPRECATED_REMOVED)
 
 #if defined(MBEDTLS_DEPRECATED_WARNING)