linuxkpi: Add typecheck.h

typecheck macro check if the type of a variable matches a type.

MFC after: 1 week
Sponsored by: Beckhoff Automation GmbH & Co. KG
Differential Revision: https://reviews.freebsd.org/D35569

(cherry picked from commit 631bf94fe9dffb48377061e5b95812990f687b3d)