libpthread/nptl: create timer thread with sufficiant stack size (account for TLS)

Create timer thread with sufficiant stack size (take into account
allocated space for thread-local-storage), for this backport glibc
commit 'Create internal threads with sufficient stack size' ([1],
[2]) introducing __pthread_get_minstack() and use it in
__start_helper_thread().

Fixes timer_create() in case of linking with library using large
TLS area (e.g openblas, see [3]).

[1] https://sourceware.org/git/?p=glibc.git;a=commitdiff;h=2c1094bd700e63a8d7f547b3f5495bedb55c0a08
[2] https://sourceware.org/git/?p=glibc.git;a=commitdiff;h=630f4cc3aa019ede55976ea561f1a7af2f068639
[3] http://lists.busybox.net/pipermail/buildroot/2021-April/308281.html

Signed-off-by: Peter Seiderer <ps.report@gmx.net>

libpthread/nptl/init.c

@@ -337,3 +337,9 @@ __pthread_initialize_minimal_internal (void)
 }
 strong_alias (__pthread_initialize_minimal_internal,
 	      __pthread_initialize_minimal)
+
+size_t
+__pthread_get_minstack (const pthread_attr_t *attr)
+{
+  return __static_tls_size + PTHREAD_STACK_MIN;
+}

libpthread/nptl/pthreadP.h

@@ -377,6 +377,7 @@ weak_function;
 
 extern void __pthread_init_static_tls (struct link_map *) attribute_hidden;
 
+extern size_t __pthread_get_minstack (const pthread_attr_t *attr);
 
 /* Namespace save aliases.  */
 extern int __pthread_getschedparam (pthread_t thread_id, int *policy,

libpthread/nptl/sysdeps/unix/sysv/linux/timer_routines.c

@@ -164,7 +164,7 @@ __start_helper_thread (void)
      and should go away automatically when canceled.  */
   pthread_attr_t attr;
   (void) pthread_attr_init (&attr);
-  (void) pthread_attr_setstacksize (&attr, PTHREAD_STACK_MIN);
+  (void) pthread_attr_setstacksize (&attr, __pthread_get_minstack (&attr));
 
   /* Block all signals in the helper thread but SIGSETXID.  To do this
      thoroughly we temporarily have to block all signals here.  The