disable AES on s390x architecture

[tmh1999]

AES is only on available on x86*

[moneromooo-monero]

It'd seem better to only enable it on the few archs we can. Let this go in, I'll open a bug for this to change.

[ghost]

AES is also available on (some) ARMv8

[hyc]

@NanoAkron yes but not using -maes flag.

[vtnerd]

Did a comment get deleted? My email is showing one that isn't coming up ... Anyway cmake has CheckCXXCompilerFlag, CheckCXXSourceCompiles, and CheckCXXSourceRuns. They are going to be tricky to use properly (false positives), so I am not sure if anyone wants to put that much effort into this. But it should be possible.

[tmh1999]

Would you mind merge this PR for now and wait for #3740 later ?

[moneromooo-monero]

It will be merged once we get to it after we start merging to master again. We will not be waiting for #3740.

[baryluk]

You should test for positive archs, not negative archs. I.e. if you go this route you might need to exclude dozen other archs. Better to list just supported archs. Or just ask compiler if it understands the flag.

@NanoAkron -maes is about AES-NI, it is only on x86 and amd64 archs. and maybe ia64. Many ARM subarchs, and even modern PPC, Power, MIPS and s390x does in fact have AES acceleration one way or another, but it is different thing.

[iamsmooth]

Maybe references to 'AES support' in the CMake should be changed to something better descriptive of what it actually does?

[luigi1111]

@tmh1999 please rebase.

[moneromooo-monero]

ping

[moneromooo-monero]

I rebased this to current master, see #4401.

[fluffypony]

Closed; cherry-picked, rebased and merged via #4401