Merge branch 'warn-exception'

Heiko Carstens says:

====================

v2:
- Use generic WARN() implementation in case of gcc-8, which avoids the need
  to raise the minimum gcc version to gcc-9 for (only) s390

- Add couple of additional ifdef guards to avoid compile errors and
  warnings

v1 ([1]):
Use the generic infrastructure introduced by Peter Zijlstra [2] to implement
an exception based WARN() and WARN_ONCE() similar to x86.

Due to some compiler oddities on s390 this requires to raise the minimum gcc
version to 9. Maybe there are ways to avoid this, but I failed to find a
working solution. Details are in the patch descriptions.

Just posting this now to also get some compile bot testing, since I'm afraid
there might be some compiler version / config option around where even this
new approach breaks.

Peter, since you were wondering: your generic infrastructure pieces work very
nice. Looking at the x86 and s390 implementation: it might be possible to make
things even more generic since both __WARN_printf(), and WARN_ONCE() are
identical; it looks like only __WARN_print_arg() needs to be provided.

[1] https://lore.kernel.org/all/20251209121701.1856271-1-hca@linux.ibm.com/
[2] https://lore.kernel.org/all/20251110114633.202485143@infradead.org/

====================

Signed-off-by: Heiko Carstens <hca@linux.ibm.com>