include mbedtls_platform_requirements.h in mbedtls_config.c

This is required because if the user defined configuration file (not the
default one provided by mbedtls) includes files from the standard
C library then __STDC_WANT_LIB_EXT1__ won't be defined there which
cause weird build failures.

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>

library/mbedtls_config.c

@@ -6,6 +6,8 @@
  *  SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later
  */
 
+#include "mbedtls_platform_requirements.h"
+
 /* We are a special snowflake: we don't include "mbedtls_common.h",
  * because that would pull <mbedtls/build_info.h> and we need to
  * tune the way it works. */