Use a portable way to initialize a recursive mutex.

--- src/eventloop.cpp	2011-11-28 16:03:19.000000000 +0100
+++ src/eventloop.cpp	2015-12-20 11:17:56.774568824 +0100
@@ -85,8 +85,11 @@
 {
   if (recursive)
   {
-    pthread_mutex_t recmutex = PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP;
-    _mutex = recmutex;
+    pthread_mutexattr_t attr;
+    pthread_mutexattr_init(&attr);
+    pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_RECURSIVE);
+    pthread_mutex_init(&_mutex, &attr);
+    pthread_mutexattr_destroy(&attr);
   }
   else
   {