lib509: add missing include for strdup

Closes https://github.com/curl/curl/pull/3739

diff --git a/tests/libtest/lib509.c b/tests/libtest/lib509.c
index 59ced355fa875cbb72b01f19685d96505798cce6..755208b8d7dc977e9216ced570ddf1775fe55db9 100644 (file)
--- a/tests/libtest/lib509.c
+++ b/tests/libtest/lib509.c
@@ -21,6 +21,8 @@
  ***************************************************************************/
 #include "test.h"
 
+#include <string.h>
+
 /*
  * This test uses these funny custom memory callbacks for the only purpose
  * of verifying that curl_global_init_mem() functionality is present in