libstdc++: testsuite: Address random failure in pthread_create() [PR54185]

The test for this PR calls pthread_create() many times in a row, which may fail
with EAGAIN sometimes. Avoid generating a test failure in this case.

libstdc++-v3/ChangeLog:

	PR libstdc++/54185
	* testsuite/30_threads/condition_variable/54185.cc: Make test robust
	to random pthread_create() failures.

diff --git a/libstdc++-v3/testsuite/30_threads/condition_variable/54185.cc b/libstdc++-v3/testsuite/30_threads/condition_variable/54185.cc
index ea0d5bb8740..cbd21e11e57 100644
--- a/libstdc++-v3/testsuite/30_threads/condition_variable/54185.cc
+++ b/libstdc++-v3/testsuite/30_threads/condition_variable/54185.cc
@@ -31,19 +31,25 @@
 std::condition_variable* cond = nullptr;
 std::mutex mx;
 int started = 0;
+bool notified = false;
 int constexpr NUM_THREADS = 10;
 
+static void finalize_cond()
+{
+  /* Lock should be held when calling this.  */
+  notified = true;
+  cond->notify_all();
+  delete cond;
+  cond = nullptr;
+}
+
 void do_thread_a()
 {
   std::unique_lock<std::mutex> lock(mx);
   if(++started >= NUM_THREADS)
-  {
-    cond->notify_all();
-    delete cond;
-    cond = nullptr;
-  }
+    finalize_cond();
   else
-    cond->wait(lock);
+    cond->wait(lock, [] { return notified; });
 }
 
 int main(){
@@ -51,11 +57,24 @@ int main(){
   for(int j = 0; j < 1000; ++j)
   {
     started = 0;
+    notified = false;
     cond = new std::condition_variable;
     for (int i = 0; i < NUM_THREADS; ++i)
-      vec.emplace_back(&do_thread_a);
-    for (int i = 0; i < NUM_THREADS; ++i)
-      vec[i].join();
+      {
+	try
+	  {
+	    vec.emplace_back(&do_thread_a);
+	  }
+	catch(const std::system_error&)
+	  {
+	    /* Thread creation may fail due to resource limits; just move on.  */
+	    std::unique_lock<std::mutex> lock(mx);
+	    finalize_cond();
+	    break;
+	  }
+      }
+    for(auto& thread: vec)
+      thread.join();
     vec.clear();
   }
 }