gh-143121: Avoid thread leak in configure (gh-143122)

If you are building with `--with-thread-sanitizer` and don't use the
suppression file, then running configure will report a thread leak.

Call `pthread_join()` to avoid the thread leak.
diff --git a/configure b/configure
index b1faeaf..411bc1a 100755
--- a/configure
+++ b/configure
@@ -18190,6 +18190,7 @@
         if (pthread_attr_init(&attr)) return (-1);
         if (pthread_attr_setscope(&attr, PTHREAD_SCOPE_SYSTEM)) return (-1);
         if (pthread_create(&id, &attr, foo, NULL)) return (-1);
+        if (pthread_join(id, NULL)) return (-1);
         return (0);
       }
 _ACEOF
diff --git a/configure.ac b/configure.ac
index 043ec95..9e63c8f 100644
--- a/configure.ac
+++ b/configure.ac
@@ -4760,6 +4760,7 @@
         if (pthread_attr_init(&attr)) return (-1);
         if (pthread_attr_setscope(&attr, PTHREAD_SCOPE_SYSTEM)) return (-1);
         if (pthread_create(&id, &attr, foo, NULL)) return (-1);
+        if (pthread_join(id, NULL)) return (-1);
         return (0);
       }]])],
       [ac_cv_pthread_system_supported=yes],