Fix name conflict and implicit use of functions from string.h
diff --git a/tests/suites/test_suite_hmac_drbg.function b/tests/suites/test_suite_hmac_drbg.function
index a413f5e..21b300e 100644
--- a/tests/suites/test_suite_hmac_drbg.function
+++ b/tests/suites/test_suite_hmac_drbg.function
@@ -1,5 +1,6 @@
 /* BEGIN_HEADER */
 #include "mbedtls/hmac_drbg.h"
+#include "string.h"
 
 typedef struct
 {