Import mbedtls-2.27.0

Imports Mbed TLS 2.27.0 from https://github.com/ARMmbed/mbedtls.git
commit f71e28780841 ("Merge pull request #843 from
paul-elliott-arm/mbedtls-2.27.0rc0-pr") (tag mbedtls-2.27.0, v2.27.0).

Files that are not needed are removed.

 cd lib/libmbedtls
 rm -rf mbedtls
 cp -R path/to/mbedtls-2.27.0/mbedtls .
 cd mbedtls
 rm CMakeLists.txt DartConfiguration.tcl Makefile
 rm .gitignore .travis.yml .pylintrc .globalrc .mypy.ini BRANCHES.md
 rm include/.gitignore include/CMakeLists.txt library/.gitignore
 rm library/CMakeLists.txt library/Makefile
 rm -rf .git .github doxygen configs programs scripts tests visualc yotta
 rm -rf 3rdparty ChangeLog.d docs
 rm -rf include/mbedtls/config_psa.h include/psa
 rm library/psa_* library/mps_*
 cd ..
 git add mbedtls

This is a complete overwrite of previous code so earlier changes in the
previous branch import/mbedtls-2.22.0 will be added on top of this commit.

Signed-off-by: Jerome Forissier <jerome@forissier.org>
diff --git a/lib/libmbedtls/mbedtls/library/threading.c b/lib/libmbedtls/mbedtls/library/threading.c
index dc7896e..2de117f 100644
--- a/lib/libmbedtls/mbedtls/library/threading.c
+++ b/lib/libmbedtls/mbedtls/library/threading.c
@@ -1,8 +1,8 @@
-// SPDX-License-Identifier: Apache-2.0
 /*
  *  Threading abstraction layer
  *
- *  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)
  */
 
 /*
@@ -27,11 +25,7 @@
 #define _POSIX_C_SOURCE 200112L
 #endif
 
-#if !defined(MBEDTLS_CONFIG_FILE)
-#include "mbedtls/config.h"
-#else
-#include MBEDTLS_CONFIG_FILE
-#endif
+#include "common.h"
 
 #if defined(MBEDTLS_THREADING_C)
 
@@ -48,7 +42,7 @@
 
 #if !( ( defined(_POSIX_VERSION) && _POSIX_VERSION >= 200809L ) ||     \
        ( defined(_POSIX_THREAD_SAFE_FUNCTIONS ) &&                     \
-         _POSIX_THREAD_SAFE_FUNCTIONS >= 20112L ) )
+         _POSIX_THREAD_SAFE_FUNCTIONS >= 200112L ) )
 /*
  * This is a convenience shorthand macro to avoid checking the long
  * preprocessor conditions above. Ideally, we could expose this macro in
@@ -63,7 +57,7 @@
 
 #endif /* !( ( defined(_POSIX_VERSION) && _POSIX_VERSION >= 200809L ) ||     \
              ( defined(_POSIX_THREAD_SAFE_FUNCTIONS ) &&                     \
-                _POSIX_THREAD_SAFE_FUNCTIONS >= 20112L ) ) */
+                _POSIX_THREAD_SAFE_FUNCTIONS >= 200112L ) ) */
 
 #endif /* MBEDTLS_HAVE_TIME_DATE && !MBEDTLS_PLATFORM_GMTIME_R_ALT */
 
@@ -73,6 +67,12 @@
     if( mutex == NULL )
         return;
 
+    /* A nonzero value of is_valid indicates a successfully initialized
+     * mutex. This is a workaround for not being able to return an error
+     * code for this function. The lock/unlock functions return an error
+     * if is_valid is nonzero. The Mbed TLS unit test code uses this field
+     * to distinguish more states of the mutex; see
+     * tests/src/threading_helpers for details. */
     mutex->is_valid = pthread_mutex_init( &mutex->mutex, NULL ) == 0;
 }