Squashed commit upgrading to mbedtls-2.27.0

Squash merging branch import/mbedtls-2.27.0

 335b95f50f90 ("core: libmbedtls: add ctr_drbg.c to core sources")
 9ad9df8b36e4 ("core: libtomcrypt: libmbedtls: mbedtls_mpi_montred() now returns void")
 ade0994c57b3 ("libmbedtls: add SM2 curve")
 3041cf9726e2 ("libmbedtls: mbedtls_mpi_exp_mod(): optimize mempool usage")
 a2e7a4cd262d ("libmbedtls: mbedtls_mpi_exp_mod(): reduce stack usage")
 87efbd27f8e0 ("libmbedtls: mbedtls_mpi_exp_mod() initialize W")
 e7c59b9b1d5f ("libmbedtls: fix no CRT issue")
 d76bd278d9e2 ("libmbedtls: add interfaces in mbedtls for context memory operation")
 e5b6c167f809 ("libmedtls: mpi_miller_rabin: increase count limit")
 b81d896a903d ("libmbedtls: add mbedtls_mpi_init_mempool()")
 3fbd8660c09d ("libmbedtls: make mbedtls_mpi_mont*() available")
 2cc759c67e37 ("mbedtls: configure mbedtls to reach for config")
 48bf81758c6e ("mbedtls: remove default include/mbedtls/config.h")
 3602df84d7b3 ("Import mbedtls-2.27.0")

Signed-off-by: Jerome Forissier <jerome@forissier.org>
Acked-by: Jens Wiklander <jens.wiklander@linaro.org>
diff --git a/lib/libmbedtls/mbedtls/library/gcm.c b/lib/libmbedtls/mbedtls/library/gcm.c
index ddd2d4e..f237bab 100644
--- a/lib/libmbedtls/mbedtls/library/gcm.c
+++ b/lib/libmbedtls/mbedtls/library/gcm.c
@@ -1,8 +1,8 @@
-// SPDX-License-Identifier: Apache-2.0
 /*
  *  NIST SP800-38D compliant GCM implementation
  *
- *  Copyright (C) 2006-2015, ARM Limited, All Rights Reserved
+ *  Copyright The Mbed TLS Contributors
+ *  SPDX-License-Identifier: Apache-2.0
  *
  *  Licensed under the Apache License, Version 2.0 (the "License"); you may
  *  not use this file except in compliance with the License.
@@ -15,8 +15,6 @@
  *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  *  See the License for the specific language governing permissions and
  *  limitations under the License.
- *
- *  This file is part of mbed TLS (https://tls.mbed.org)
  */
 
 /*
@@ -29,11 +27,7 @@
  * [MGV] 4.1, pp. 12-13, to enhance speed without using too much memory.
  */
 
-#if !defined(MBEDTLS_CONFIG_FILE)
-#include "mbedtls/config.h"
-#else
-#include MBEDTLS_CONFIG_FILE
-#endif
+#include "common.h"
 
 #if defined(MBEDTLS_GCM_C)
 
@@ -825,6 +819,15 @@
                                 add_len_test_data[i],
                                 pt_test_data[pt_index_test_data[i]],
                                 buf, 16, tag_buf );
+#if defined(MBEDTLS_GCM_ALT)
+            /* Allow alternative implementations to only support 12-byte nonces. */
+            if( ret == MBEDTLS_ERR_PLATFORM_FEATURE_UNSUPPORTED &&
+                iv_len_test_data[i] != 12 )
+            {
+                mbedtls_printf( "skipped\n" );
+                break;
+            }
+#endif /* defined(MBEDTLS_GCM_ALT) */
             if( ret != 0 )
                 goto exit;