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/common.h b/lib/libmbedtls/mbedtls/library/common.h
new file mode 100644
index 0000000..5845766
--- /dev/null
+++ b/lib/libmbedtls/mbedtls/library/common.h
@@ -0,0 +1,53 @@
+/**
+ * \file common.h
+ *
+ * \brief Utility macros for internal use in the library
+ */
+/*
+ *  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.
+ *  You may obtain a copy of the License at
+ *
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+
+#ifndef MBEDTLS_LIBRARY_COMMON_H
+#define MBEDTLS_LIBRARY_COMMON_H
+
+#if defined(MBEDTLS_CONFIG_FILE)
+#include MBEDTLS_CONFIG_FILE
+#else
+#include "mbedtls/config.h"
+#endif
+
+/** Helper to define a function as static except when building invasive tests.
+ *
+ * If a function is only used inside its own source file and should be
+ * declared `static` to allow the compiler to optimize for code size,
+ * but that function has unit tests, define it with
+ * ```
+ * MBEDTLS_STATIC_TESTABLE int mbedtls_foo(...) { ... }
+ * ```
+ * and declare it in a header in the `library/` directory with
+ * ```
+ * #if defined(MBEDTLS_TEST_HOOKS)
+ * int mbedtls_foo(...);
+ * #endif
+ * ```
+ */
+#if defined(MBEDTLS_TEST_HOOKS)
+#define MBEDTLS_STATIC_TESTABLE
+#else
+#define MBEDTLS_STATIC_TESTABLE static
+#endif
+
+#endif /* MBEDTLS_LIBRARY_COMMON_H */