[newlib-cygwin/cygwin-3_4-branch] Cygwin: thread: Reset _my_tls.tid if it's pthread_null in init_mainthread().

[Takashi Yano <tyan0@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=fcaa1c496768f0781fe7515852ff7dc3bda67e78

commit fcaa1c496768f0781fe7515852ff7dc3bda67e78
Author: Takashi Yano <takashi.yano@nifty.ne.jp>
Date:   Fri Jun 23 00:07:26 2023 +0900

    Cygwin: thread: Reset _my_tls.tid if it's pthread_null in init_mainthread().
    
    Currently, _my_tls.tid is set to pthread_null if pthread::self()
    is called before pthread::init_mainthread(). As a result, pthread::
    init_mainthread() does not set _my_tls.tid appropriately. Due to
    this, pthread_join() fails in LDAP environment if the program is
    the first program which loads cygwin1.dll.
    
    https://cygwin.com/pipermail/cygwin/2023-June/253792.html
    
    With this patch, _my_tls.tid is re-initialized in pthread::
    init_mainthread() if it is pthread_null.
    
    Reported-by: Mümin A. <muminaydin06@gmail.com>
    Reviewed-by: Corinna Vinschen <corinna@vinschen.de>
    Signed-off-by: Takashi Yano <takashi.yano@nifty.ne.jp>

Diff:
---
 winsup/cygwin/thread.cc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/winsup/cygwin/thread.cc b/winsup/cygwin/thread.cc
index 5c1284a93..f614e01c4 100644
--- a/winsup/cygwin/thread.cc
+++ b/winsup/cygwin/thread.cc
@@ -364,7 +364,7 @@ void
 pthread::init_mainthread ()
 {
   pthread *thread = _my_tls.tid;
-  if (!thread)
+  if (!thread || thread == pthread_null::get_null_pthread ())
     {
       thread = new pthread ();
       if (!thread)