Find a way to test auxv on Linux

[gnzlbg]

Ideally we should add some synthetic tests like the ones for cpuinfo that works on all platforms. The auxv crate has some of them here: https://bitbucket.org/marshallpierce/rust-auxv/src/8d07bcd24d72f35ab3a610fb022dc5988a9ce210/src/test-data/?at=master (@marshallpierce)

but none of them are for ARM or PowerPC which are the only platforms were we currently use auxv.

[marshallpierce]

I added a procfs auxv file from my raspberry pi 3 to that repo, so now there's at least an arm sample.

[gnzlbg]

Nice! That is very helpful! As a rough sketch of what we could initially do, how does the following sound?:

• add the auxv crate as a dev-dependency and test that our implementation produces the same results as the auxv crate on all the platforms that we are currently testing
• test directly against some or all of the auxv dumps of the auxv crate (I don't know the best way to set this up, but worst case we can just copy the files here)
• generate dumps of auxv for other platforms that we care about and commit them to the auxv crate upstream

[marshallpierce]

Sounds good to me!

[gnzlbg]

This has already been fixed on master. We test run-time detection against the auxv crate and some processor dumps for ARM, Aarch64, and PowerPC.