x86: get rid of TIF_IRET hackery

TIF_NOTIFY_RESUME will work in precisely the same way; all that
is achieved by TIF_IRET is appearing that there's some work to be
done, so we end up on the iret exit path.  Just use NOTIFY_RESUME.
And for execve() do that in 32bit start_thread(), not sys_execve()
itself.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
index 516fa18..75fcad1 100644
--- a/arch/x86/kernel/process_32.c
+++ b/arch/x86/kernel/process_32.c
@@ -194,6 +194,11 @@
 	 * Free the old FP and other extended state
 	 */
 	free_thread_xstate(current);
+	/*
+	 * force it to the iret return path by making it look as if there was
+	 * some work pending.
+	 */
+	set_thread_flag(TIF_NOTIFY_RESUME);
 }
 EXPORT_SYMBOL_GPL(start_thread);