KVM: selftests: Use pattern matching in .gitignore

KVM: selftests: Use pattern matching in .gitignore

Use pattern matching to exclude everything except .c, .h, .S, and .sh
files from Git.  Manually adding every test target has an absurd
maintenance cost, is comically error prone, and leads to bikeshedding
over whether or not the targets should be listed in alphabetical order.

Deliberately do not include the one-off assets, e.g. config, settings,
.gitignore itself, etc as Git doesn't ignore files that are already in
the repository.  Adding the one-off assets won't prevent mistakes where
developers forget to --force add files that don't match the "allowed".

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20221213001653.3852042-5-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>