tests: prevent inclusion of time.h in baremetal compiles

baremetal compiles should not include time.h, as MBEDTLS_HAVE_TIME is
undefined. To test this, provide an overriding include directory that
has a time.h which throws a meaningful error if included.

Signed-off-by: Daniel Axtens <dja@axtens.net>

tests/include/baremetal-override/time.h

@@ -0,0 +1,18 @@
+/*
+ *  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.
+ */
+
+#error "time.h included in a configuration without MBEDTLS_HAVE_TIME"

tests/scripts/all.sh

@@ -1507,9 +1507,15 @@ component_build_crypto_full () {
 component_build_crypto_baremetal () {
   msg "build: make, crypto only, baremetal config"
   scripts/config.py crypto_baremetal
-  make CFLAGS='-O1 -Werror'
+  make CFLAGS="-O1 -Werror -I$(pwd)/tests/include/baremetal-override/"
   are_empty_libraries library/libmbedx509.* library/libmbedtls.*
 }
+support_build_crypto_baremetal () {
+    # Older Glibc versions include time.h from other headers such as stdlib.h,
+    # which makes the no-time.h-in-baremetal check fail. Ubuntu 16.04 has this
+    # problem, Ubuntu 18.04 is ok.
+    ! grep -q -F time.h /usr/include/x86_64-linux-gnu/sys/types.h
+}
 
 component_test_depends_curves () {
     msg "test/build: curves.pl (gcc)" # ~ 4 min