Log Message:
Update xenkernel418 and xentools418 to 20240909. This brings in Xen 4.18.3

pkgsrc CHANGES:
set O_CLOEXEC (if requested) and remove O_NONBLOCK on /dev/xenevt
set O_CLOEXEC on /kern/xen/privcmd
(both from the freebsd-specific code)

Main changes since 20231116 (Xen 4.18.0):
Fix various bugs, especially in these areas:
- interrupt setup
- error paths

better support for some of the newer CPUs
some performances improvement

Fixes XSA-447, XSA-449, XSA-450, XSA-451, XSA-452, XSA-453, XSA-454, XSA-455,
      XSA-456, XSA-458, XSA-460, XSA-461