KVM selftests fixes for 6.8 merge window:

 - Fix an annoying goof where the NX hugepage test prints out garbage
   instead of the magic token needed to run the text.

 - Fix build errors when a header is delete/moved due to a missing flag
   in the Makefile.

 - Detect if KVM bugged/killed a selftest's VM and print out a helpful
   message instead of complaining that a random ioctl() failed.

 - Annotate the guest printf/assert helpers with __printf(), and fix the
   various bugs that were lurking due to lack of said annotation.

A small subset of these was included in 6.7-rc as well.