POSIX threads don't use errno to report errors

Fix simple_semaphore to follow POSIX threads convention for reporting
errors.

src/err.hpp

@@ -22,6 +22,7 @@
 
 #include <assert.h>
 #include <errno.h>
+#include <string.h>
 #include <stdlib.h>
 #include <stdio.h>
 
@@ -81,10 +82,10 @@ namespace zmq
 }} while (false)
 
 // Provides convenient way to check for POSIX errors.
-#define posix_assert(x) do {\
-fprintf (stderr, "%s (%s:%d)\n", strerror (x), __FILE__, __LINE__);\
-abort ();\
-} while (false)
+#define posix_assert(x) do { if ((x)) {\
+    fprintf (stderr, "%s (%s:%d)\n", strerror (x), __FILE__, __LINE__);\
+    abort ();\
+}} while (false)
 
 // Provides convenient way to check for errors from getaddrinfo.
 #define gai_assert(x) do { if (x) {\

src/simple_semaphore.hpp

@@ -53,32 +53,32 @@ namespace zmq
         inline simple_semaphore_t ()
         {
             int rc = pthread_mutex_init (&mutex, NULL);
-	    errno_assert (rc == 0);
+            posix_assert (rc);
             rc = pthread_mutex_lock (&mutex);
-	    errno_assert (rc == 0);
+            posix_assert (rc);
         }
 
         //  Destroy the semaphore.
         inline ~simple_semaphore_t ()
         {
             int rc = pthread_mutex_unlock (&mutex);
-            errno_assert (rc == 0);
+            posix_assert (rc);
             rc = pthread_mutex_destroy (&mutex);
-            errno_assert (rc == 0);
+            posix_assert (rc);
         }
 
         //  Wait for the semaphore.
         inline void wait ()
         {
              int rc = pthread_mutex_lock (&mutex);
-             errno_assert (rc == 0);
+             posix_assert (rc);
         }
 
         //  Post the semaphore.
         inline void post ()
         {
             int rc = pthread_mutex_unlock (&mutex);
-            errno_assert (rc == 0);
+            posix_assert (rc);
         }
 
     private: