linux: adjust ordering of Linux auxv and add dummy AT_HWCAP2

[trasz]

Summary

This should be a no-op; the purpose of this is to reduce
a spurious difference between Linuxulator and Linux, to make
debugging slightly easier.

Note that AT_HWCAP2 we pass to Linux binaries is always 0,
instead of being equal to 'cpu_feature2'. This matches what
I've observed under Ubuntu Focal VM.

[chuck]

LGTM