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/onefile.c b/programs/fuzz/onefile.c
index 2d4330a..6c02a64 100644
--- a/programs/fuzz/onefile.c
+++ b/programs/fuzz/onefile.c
@@ -1,3 +1,5 @@
+#define MBEDTLS_DECLARE_PRIVATE_IDENTIFIERS
+
 #include <stdint.h>
 #include <stdlib.h>
 #include <stdio.h>