lkdtm: Make arch-specific tests always available

lkdtm: Make arch-specific tests always available

I'd like arch-specific tests to XFAIL when on a mismatched architecture
so that we can more easily compare test coverage across all systems.
Lacking kernel configs or CPU features count as a FAIL, not an XFAIL.

Additionally fixes a build failure under 32-bit UML.

Fixes: b09511c253e5 ("lkdtm: Add a DOUBLE_FAULT crash type on x86")
Fixes: cea23efb4de2 ("lkdtm/bugs: Make double-fault test always available")
Fixes: 6cb6982f42cb ("lkdtm: arm64: test kernel pointer authentication")
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20200625203704.317097-5-keescook@chromium.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>