Using generated/compile.h triggered a full LKDTM rebuild with every
build. Avoid this by using the exported strings instead.

Fixes: b8661450 ("lkdtm: Add kernel version to failure hints")
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20210901233406.2571643-1-keescook@chromium.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>