stdlib: resolve a double lock init issue after fork [BZ #32994]

The __abort_fork_reset_child (introduced in
d40ac01cbb) call resets the lock after the
fork. This causes a DRD regression in valgrind
(https://bugs.kde.org/show_bug.cgi?id=503668), as it's effectively a
double initialization, despite it being actually ok in this case. As
suggested in https://sourceware.org/bugzilla/show_bug.cgi?id=32994#c2
we replace it here with a memcpy of another initialized lock instead,
which makes valgrind happy.

Reviewed-by: Florian Weimer <fweimer@redhat.com>

stdlib/abort.c

@@ -19,6 +19,7 @@
 #include <internal-signals.h>
 #include <libc-lock.h>
 #include <pthreadP.h>
+#include <string.h>
 #include <unistd.h>
 
 /* Try to get a machine dependent instruction which will make the
@@ -42,7 +43,10 @@ __libc_rwlock_define_initialized (static, lock);
 void
 __abort_fork_reset_child (void)
 {
-  __libc_rwlock_init (lock);
+  /* Reinitialize lock without calling pthread_rwlock_init, to
+     avoid a valgrind DRD false positive.  */
+  __libc_rwlock_define_initialized (, reset_lock);
+  memcpy (&lock, &reset_lock, sizeof (lock));
 }
 
 void