Start from a clean baseline for C11 ext1 and POSIX features

Define `_POSIX_C_SOURCE` and `_XOPEN_SOURCE` in a single place that
applies everywhere, to make things simple.

This may break some platforms that require special handling for POSIX
functions and types. Subsequent commits will add platform-specific hacks
as needed.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

library/mbedtls_platform_requirements.h

@@ -15,6 +15,20 @@
 #ifndef MBEDTLS_MBEDTLS_PLATFORM_REQUIREMENTS_H
 #define MBEDTLS_MBEDTLS_PLATFORM_REQUIREMENTS_H
 
+#if !defined(_POSIX_C_SOURCE)
+/* For standards-compliant access to
+ * getaddrinfo(),
+ * ... */
+#define _POSIX_C_SOURCE 200112L
+#endif
+
+#if !defined(_XOPEN_SOURCE)
+/* For standards-compliant access to
+ * sockaddr_storage,
+ * ... */
+#define _XOPEN_SOURCE 600
+#endif
+
 /* On Mingw-w64, force the use of a C99-compliant printf() and friends.
  * This is necessary on older versions of Mingw and/or Windows runtimes
  * where snprintf does not always zero-terminate the buffer, and does

library/net_sockets.c

@@ -5,16 +5,6 @@
  *  SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later
  */
 
-/* Enable definition of getaddrinfo() even when compiling with -std=c99. Must
- * be set before mbedtls_config.h, which pulls in glibc's features.h indirectly.
- * Harmless on other platforms. */
-#ifndef _POSIX_C_SOURCE
-#define _POSIX_C_SOURCE 200112L
-#endif
-#ifndef _XOPEN_SOURCE
-#define _XOPEN_SOURCE 600 /* sockaddr_storage */
-#endif
-
 #include "ssl_misc.h"
 
 #if defined(MBEDTLS_NET_C)