This returns the `XFEATURE_ENABLED_MASK` register which reports what
features are enabled on the CPU.
This behaves similarly to CPUID where it uses an index register in ecx.
This is a prerequisite to enabling XSAVE/XRSTOR and AVX since
applications will expect this to exist.
xsetbv is a privileged instruction and doesn't need to be implemented.
For these unit tests we no longer need to put them in the disabled tests
file. Instead it will be skipped if the host doesn't support the feature
required.
First test just ensures that an aligned cacheline clear will clear out
the data.
Second test ensures an unaligned address will still only clear the
cacheline the address lies in without touching the other surrounding
cachelines.
Disabled on the host runner since the CI host runner doesn't support the
instruction
