Cygwin: dll_init: Don't call dll::init() twice for DLL_LOAD.

If dlopen() for DLL A is called in constructor DLL B, the constructor
for DLL A is called twice, once called via cygwin_attach_dll() called
from LoadLibrary(), and again from dll_list::init(). That is, the DLL
with DLL_LOAD does not need dll::init() in dll_list::init(). This issue
was found when debugging the issue:
https://cygwin.com/pipermail/cygwin/2025-October/258877.html
This patch remove dll::init() call in dll_list::init() for DLL_LOAD.

Fixes: 2eb392b ("dll_init.cc: Revamp.  Use new classes.")
Reviewed-by: Mark Geisert <mark@maxrnd.com>, Jon Turney <jon.turney@dronecode.org.uk>, Corinna Vinschen <corinna-cygwin@cygwin.com>
Signed-off-by: Takashi Yano <takashi.yano@nifty.ne.jp>
(cherry picked from commit d77cb8e)

Author: tyan0

winsup/cygwin/dll_init.cc

@@ -618,9 +618,10 @@ dll_list::init ()
   /* Walk the dll chain, initializing each dll */
   dll *d = &start;
   dll_global_dtors_recorded = d->next != NULL;
-  /* Init linked and early loaded Cygwin DLLs. */
+  /* Init linked Cygwin DLLs. As for loaded DLLs, dll::init() is already
+     called via _cygwin_dll_entry called from LoadLibrary(). */
   while ((d = d->next))
-    if (d->type == DLL_LINK || d->type == DLL_LOAD)
+    if (d->type == DLL_LINK)
       d->init ();
 }