Can't compile applications using libprojectM due to missing header

[ericonr]

Hi! f7f74b1 seems to have reorganized a bunch of stuff, which included switching from using the __SSE2__ macro to your own _HAS_SSE2_ one, using a dedicated header to (I assume) avoid duplicating code.

Unfortunately, the new Intrinsics.h header was included directly in Common.h, but isn't installed, which lead to build failures for applications which can link to a system projectM (in our case, the clementine player and qmmp).

I don't know if the preferred course of action is installing the new header or making it internal only (which IMO would be better, since it seems to be only an implementation detail), so I'm not opening a PR for now.

[revmischa]

Thanks for the report, I just ran into this myself. You're entirely right. That file ended up being pointless anyway. I was trying to work around multi-arch compilation issues for amd64/aarch64 for macOS but this didn't help.
I've reverted the change and done away with Intrinsics.h - b3c3282
I wasn't aware of qmmp, please add it to the README!
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