gh-137390: Add missing line continuation character in configure.ac (GH-137391)

(cherry picked from commit 001461a)

Co-authored-by: markmcclain <markmcclain@users.noreply.github.com>

Author: markmcclain

configure.ac

@@ -5228,7 +5228,7 @@ AC_CHECK_FUNCS([ \
   posix_spawn_file_actions_addclosefrom_np \
   pread preadv preadv2 process_vm_readv \
   pthread_cond_timedwait_relative_np pthread_condattr_setclock pthread_init \
-  pthread_kill pthread_get_name_np pthread_getname_np pthread_set_name_np
+  pthread_kill pthread_get_name_np pthread_getname_np pthread_set_name_np \
   pthread_setname_np pthread_getattr_np \
   ptsname ptsname_r pwrite pwritev pwritev2 readlink readlinkat readv realpath renameat \
   rtpSpawn sched_get_priority_max sched_rr_get_interval sched_setaffinity \