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/fuzz/fuzz_dtlsclient.c b/programs/fuzz/fuzz_dtlsclient.c
index 6581dcb..e667d8b 100644
--- a/programs/fuzz/fuzz_dtlsclient.c
+++ b/programs/fuzz/fuzz_dtlsclient.c
@@ -1,3 +1,5 @@
+#define MBEDTLS_DECLARE_PRIVATE_IDENTIFIERS
+
 #include <string.h>
 #include <stdlib.h>
 #include <stdint.h>