Fix compilation with gcc -std=c89

ChangeLog

 2018-12-26  Niels Möller  <nisse@lysator.liu.se>
 
+	* tools/nettle-pbkdf2.c: Add #define _GNU_SOURCE, needed for
+	strdup with gcc -std=c89.
+	* testsuite/ed25519-test.c: Add #define _GNU_SOURCE, needed for
+	getline with gcc -std=c89.
+
 	* rsa-sign-tr.c (sec_equal): Fix accidental use of C99 for loop.
 	Reported by Andreas Gustafsson.
 	* testsuite/rsa-sec-decrypt-test.c (test_main): Likewise.

testsuite/ed25519-test.c

@@ -29,6 +29,8 @@
    not, see http://www.gnu.org/licenses/.
 */
 
+#define _GNU_SOURCE
+
 #include "testutils.h"
 
 #include <errno.h>

tools/nettle-pbkdf2.c

@@ -31,6 +31,8 @@
    not, see http://www.gnu.org/licenses/.
 */
 
+#define _GNU_SOURCE
+
 #if HAVE_CONFIG_H
 # include "config.h"
 #endif