Bug#28690 mysql-enterprise-gpl-5.0.40-linux-i686-glibc won't start on Debian Sarge

 - Only use the "hack for bug in NTPL" if using NTPL, by dynamically
   checking the thd_lib_detected flag


mysys/my_thr_init.c:
  Only start the "dummy thread hack for bug in NPTL" - if using NPTL.
  If the system uses LinuxThreads it's not needed, it actually causes 
  the "pthread manager" to be started as root and thus all subsequent
  threads will also run as root although mysqld drops root privileges, 
  this in turns causes mysqld to deadlock since the mysqlds main thread
  running as <user> can't send signals to a process owned by root.

mysys/my_thr_init.c

@@ -87,27 +87,31 @@ my_bool my_thread_global_init(void)
     fprintf(stderr,"Can't initialize threads: error %d\n", pth_ret);
     return 1;
   }
-  
-#ifdef NPTL_PTHREAD_EXIT_BUG
-
-/*
-  BUG#24507: Race conditions inside current NPTL pthread_exit() implementation.
 
-  To avoid a possible segmentation fault during concurrent executions of 
-  pthread_exit(), a dummy thread is spawned which initializes internal variables
-  of pthread lib. See bug description for thoroughfull explanation. 
-  
-  TODO: Remove this code when fixed versions of glibc6 are in common use. 
-*/
+#ifdef NPTL_PTHREAD_EXIT_BUG
+  /*
+    BUG#24507: Race conditions inside current NPTL pthread_exit()
+    implementation.
 
-  pthread_t       dummy_thread;
-  pthread_attr_t  dummy_thread_attr;
+    To avoid a possible segmentation fault during concurrent
+    executions of pthread_exit(), a dummy thread is spawned which
+    initializes internal variables of pthread lib. See bug description
+    for a full explanation.
 
-  pthread_attr_init(&dummy_thread_attr);
-  pthread_attr_setdetachstate(&dummy_thread_attr,PTHREAD_CREATE_DETACHED);
+    TODO: Remove this code when fixed versions of glibc6 are in common
+    use.
+  */
+  if (thd_lib_detected == THD_LIB_NPTL)
+  {
+    pthread_t       dummy_thread;
+    pthread_attr_t  dummy_thread_attr;
 
-  pthread_create(&dummy_thread,&dummy_thread_attr,nptl_pthread_exit_hack_handler,NULL);
+    pthread_attr_init(&dummy_thread_attr);
+    pthread_attr_setdetachstate(&dummy_thread_attr, PTHREAD_CREATE_DETACHED);
 
+    pthread_create(&dummy_thread,&dummy_thread_attr,
+                   nptl_pthread_exit_hack_handler, NULL);
+  }
 #endif
 
 #ifdef PTHREAD_ADAPTIVE_MUTEX_INITIALIZER_NP