Use empty decision and reason for such kind of checks

These are very slow debugging features

Don't normalize this option value since the Linux kernel
doesn't use kstrtobool() for it.

Don't add CmdlineChecks in add_kconfig_checks() to avoid wrong results
when the tool doesn't check the cmdline.

A common pattern for checking the 'param_x' cmdline parameter
that __overrides__ the 'PARAM_X_DEFAULT' kconfig option:
  l += [OR(CmdlineCheck(reason, decision, 'param_x', '1'),
           AND(KconfigCheck(reason, decision, 'PARAM_X_DEFAULT_ON', 'y'),
               CmdlineCheck(reason, decision, 'param_x, 'is not set')))]

Here we don't check the kconfig options or minimal kernel version
required for the cmdline parameters. That would make the checks
very complex and not give a 100% guarantee anyway.

Having HARDENED_USERCOPY_FALLBACK disabled is not enough.

The Linux kernel 4.16-4.17 has a weird STACKPROTECTOR configuration:
CC_STACKPROTECTOR_NONE -- stackprotector is disabled;
CC_STACKPROTECTOR_REGULAR -- similar to current STACKPROTECTOR;
CC_STACKPROTECTOR_STRONG -- similar to current STACKPROTECTOR_STRONG;
CC_STACKPROTECTOR_AUTO -- the best stack-protector that compiler provides.
These options are mutually exclusive.

Let's improve the STACKPROTECTOR check:
- Add CC_STACKPROTECTOR_REGULAR as a valid alternative name of this option;
- Add CC_STACKPROTECTOR_STRONG to avoid false negative result;
- Add CC_STACKPROTECTOR_AUTO hoping that it enables at least STACKPROTECTOR.

The STACKPROTECTOR_STRONG check still requires explicit configuration, not
CC_STACKPROTECTOR_AUTO.

Thanks to @izh1979 for the idea

I can't recommend disabling it, because LKDTM is used to test the kernel
hardening features.

But I cant recommend enabling it, because LKDTM contains intentional
memory corruption errors. It's not for production systems.

So let's simply drop the comment about LKDTM.

#68

Use the presence check for slab_nomerge.
Also check that slab_merge is not set.

Reusing "is not set" for CmdlineCheck is a nice hack.

Nice!

populate_with_data() must be called after all checks have been added.

Thanks to the coverage info