Define MBEDTLS_DECLARE_PRIVATE_IDENTIFIERS in every sample program

Add #define MBEDTLS_DECLARE_PRIVATE_IDENTIFIERS to every sample program
before the first include so that mbedtls doesn't break with future
privatization work.

Signed-off-by: Felix Conway <felix.conway@arm.com>
diff --git a/programs/ssl/ssl_mail_client.c b/programs/ssl/ssl_mail_client.c
index bdeef9b..d3354ca 100644
--- a/programs/ssl/ssl_mail_client.c
+++ b/programs/ssl/ssl_mail_client.c
@@ -11,6 +11,8 @@
 
 #define _POSIX_C_SOURCE 200112L
 #define _XOPEN_SOURCE 600
+#define MBEDTLS_DECLARE_PRIVATE_IDENTIFIERS
+
 
 #include "mbedtls/build_info.h"