posh.h add Aarch64 support

[susnux]

This is a patch from the openSUSE games repository to enable Aarch64 support.

[BenjamenMeyer]

Are there any options that need to be added to the CMakeLists.txt as well?
See https://github.com/vegastrike/Vega-Strike-Engine-Source/blob/master/engine/CMakeLists.txt#L558 for custom options set for the various architectures (note: it is out of date in that many newer architectures are not present).

[susnux]

Are there any options that need to be added to the CMakeLists.txt as well?

Need? No. Could? Yes.
But as with x86 there are so many different configurations outside, even x86 options are not complete or up-to-date.
E.g. you could add armv7 NEON extension, or NEON2, or ARMv8-A Advanced SIMD...

But if you think this is options are useful and relevant, I can have a look into this.

[BenjamenMeyer]

@susnux I'm not sure...the compilers generally do more of that now; personally I'm not positive we even need the ones that were specified originally; just wanted to verify that something more isn't required to match it all up

[BenjamenMeyer]

Do note that while this will help with AARCH64 systems they're not presently on our targetted list of supported system. I guess we'll need to add it for M1 Mac Support; but we'll also need a CI environment for it too.