Support UB and arm64 for AAX on Mac

[p0nce]

This would allow:

• to solve #586 => nope
• to enable LV2 and AAX in multi-arch, such as arm64 and x86_64 on macOS => blocked, waiting for arm64 AAX
• 32-bit LV2 FWIW => OK It is necessary anyway for AAX Universal Binary support.

[p0nce]

What do in cases like "LV2 -a x86 is asked for, but dplug-build is -a x86_64"?

[p0nce]

• [x] Enable Windows + 32-bit + LV2
• [x] Enable Windows + 32-bit + AAX => well, this could be enabled, but is a net negative since PT10 is almost extinct. But preset reuse is implemented.
• [x] Enable Mac + arm64 + AAX => waiting for PACE and Protools
• [x] Enable Mac + UB+ AAX => waiting for PACE and Protools
• [x] tell all that in README

[p0nce]

Latest PACE should support arm64, but still in beta...

[p0nce]

Apparently Pro tools is not yet native arm64

[p0nce]

Still not native arm64... but you can build arm64 AAX and UB2, that you then can't test

[p0nce]

Now fixed, dplug-build built with arm64 cannot do UB2 builds though.