LinuxKPI: kunit: add static_stub.h and more dummy headers

These came up during a wifi driver update.

Sponsored by:	The FreeBSD Foundation (initially)
MFC after:	3 days
Reviewed by:	dumbbell
Differential Revision:	https://reviews.freebsd.org/D52079

Author: Bjoern A. Zeeb

sys/compat/linuxkpi/common/include/kunit/static_stub.h

@@ -0,0 +1,15 @@
+/*
+ * Copyright (c) 2025 The FreeBSD Foundation
+ *
+ * This software was developed by Björn Zeeb under sponsorship from
+ * the FreeBSD Foundation.
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#ifndef	_LINUXKPI_KUNIT_STATIC_STUB_H
+#define	_LINUXKPI_KUNIT_STATIC_STUB_H
+
+#define	KUNIT_STATIC_STUB_REDIRECT(_fn, ...)	do { } while(0)
+
+#endif	/* _LINUXKPI_KUNIT_STATIC_STUB_H */