define _GNU_SOURCE via autoconf

configure.ac

@@ -3,6 +3,7 @@ m4_ifndef([m4_esyscmd_s], [m4_define([m4_chomp_all], [m4_format([[%.*s]], m4_bre
 m4_ifndef([m4_esyscmd_s], [m4_define([m4_esyscmd_s], [m4_chomp_all(m4_esyscmd([$1]))])])
 AC_PREREQ([2.63])
 AC_INIT([ebusd], m4_esyscmd_s([cat VERSION]), [ebusd@ebusd.eu], [ebusd], [https://github.com/john30/ebusd])
+AC_GNU_SOURCE
 
 AC_CONFIG_AUX_DIR([build])
 AC_CONFIG_MACRO_DIR([m4])

src/lib/utils/log.cpp

@@ -16,7 +16,9 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 
-#define _GNU_SOURCE
+#ifdef HAVE_CONFIG_H
+#  include <config.h>
+#endif
 
 #include "lib/utils/log.h"
 #include <stdlib.h>

src/lib/utils/thread.cpp

@@ -20,10 +20,6 @@
 #  include <config.h>
 #endif
 
-#ifdef HAVE_PTHREAD_SETNAME_NP
-#  define _GNU_SOURCE
-#endif
-
 #include "lib/utils/thread.h"
 #include "lib/utils/clock.h"