Don't explicitly set clone child ptrace options

linux_handle_extended_wait calls target_post_attach if we're handling
a PTRACE_EVENT_CLONE, and libthread_db.so isn't active.
target_post_attach just calls linux_init_ptrace_procfs to set the
lwp's ptrace options.  However, this is completely unnecessary,
because, as man ptrace [1] says, options are inherited:

  "Flags are inherited by new tracees created and "auto-attached" via
   active PTRACE_O_TRACEFORK, PTRACE_O_TRACEVFORK, or PTRACE_O_TRACECLONE
   options."

This removes the unnecessary call.

[1] - https://man7.org/linux/man-pages/man2/ptrace.2.html

Approved-By: Simon Marchi <simon.marchi@efficios.com>
Change-Id: I533eaa60b700f7e40760311fc0d344d0b3f19a78

gdb/linux-nat.c

diff --git a/gdb/linux-nat.c b/gdb/linux-nat.c
index f4f7aa8..0b3c143 100644
--- a/gdb/linux-nat.c
+++ b/gdb/linux-nat.c
@@ -1912,7 +1912,6 @@ linux_handle_extended_wait (struct lwp_info *lp, int status)
 	    {
 	      /* The process is not using thread_db.  Add the LWP to
 		 GDB's list.  */
-	      target_post_attach (new_lp->ptid.lwp ());
 	      add_thread (linux_target, new_lp->ptid);
 	    }