Cygwin: signal: Do not handle signal when __SIGFLUSHFAST is sent

The commit a22a0ad was not entirely correct. Even with the patch,
some hangs still occur. This patch overrides the previous commit along
with the patch that makes cygwait() reentrant, to fix these hangs.

Addresses: https://cygwin.com/pipermail/cygwin/2024-December/256954.html
Fixes: d243e51 ("Cygwin: signal: Fix deadlock between main thread and sig thread")
Reported-by: Daisuke Fujimura <booleanlabel@gmail.com>
Reviewed-by: Corinna Vinschen <corinna@vinshcen.de>
Signed-off-by: Takashi Yano <takashi.yano@nifty.ne.jp>
(cherry picked from commit 83afe3e)

Author: tyan0

winsup/cygwin/sigproc.cc

@@ -742,6 +742,9 @@ sig_send (_pinfo *p, siginfo_t& si, _cygtls *tls)
       memcpy (p, si._si_commune._si_str, n); p += n;
     }
 
+  unsigned cw_mask;
+  cw_mask = pack.si.si_signo == __SIGFLUSHFAST ? 0 : cw_sig_restart;
+
   DWORD nb;
   BOOL res;
   /* Try multiple times to send if packsize != nb since that probably
@@ -751,8 +754,7 @@ sig_send (_pinfo *p, siginfo_t& si, _cygtls *tls)
       res = WriteFile (sendsig, leader, packsize, &nb, NULL);
       if (!res || packsize == nb)
 	break;
-      if (cygwait (NULL, 10, cw_sig_eintr) == WAIT_SIGNALED)
-	_my_tls.call_signal_handler ();
+      cygwait (NULL, 10, cw_mask);
       res = 0;
     }
 
@@ -785,7 +787,7 @@ sig_send (_pinfo *p, siginfo_t& si, _cygtls *tls)
   if (wait_for_completion)
     {
       sigproc_printf ("Waiting for pack.wakeup %p", pack.wakeup);
-      rc = cygwait (pack.wakeup, WSSC);
+      rc = cygwait (pack.wakeup, WSSC, cw_mask);
       ForceCloseHandle (pack.wakeup);
     }
   else
@@ -806,9 +808,6 @@ sig_send (_pinfo *p, siginfo_t& si, _cygtls *tls)
       rc = -1;
     }
 
-  if (wait_for_completion && si.si_signo != __SIGFLUSHFAST)
-    _my_tls.call_signal_handler ();
-
 out:
   if (communing && rc)
     {