um: move thread info into task

This selects the THREAD_INFO_IN_TASK option for UM and changes the way
that the current task is discovered. This is trivial though, as UML
already tracks the current task in cpu_tasks[] and this can be used to
retrieve it.

Also remove the signal handler code that copies the thread information
into the IRQ stack. It is obsolete now, which also means that the
mentioned race condition cannot happen anymore.

Signed-off-by: Benjamin Berg <benjamin.berg@intel.com>
Reviewed-by: Hajime Tazaki <thehajime@gmail.com>
Link: https://patch.msgid.link/20241111102910.46512-1-benjamin@sipsolutions.net


Signed-off-by: Johannes Berg <johannes.berg@intel.com>