improve x86 AVX/SSE detection on *BSD

[jg1uaa]

current AVX2/AVX/SSE4.1 detection method for Linux/*BSD works on Linux and NetBSD.
FreeBSD/DragonFlyBSD/OpenBSD needs different approach so I add it for x86/amd64. For aarch32/64, using CMAKE_SYSTEM_PROCESSOR solves these platform but this is not implemented because I don't have any working *BSD on arm processor.

[drowe67]

Hi @jg1uaa - we aren't maintaining this repo any more as we are focused on RADE which outperforms all the FreeDV 2020 modes.

[jg1uaa]

freedv-gui's build_linux.sh refers this repo directly.
https://github.com/drowe67/freedv-gui/blob/master/build_linux.sh#L32
even if LPCNet will be deprecated, this small fix is required for whom try to use this on *BSDs.

[drowe67]

Do you have any evidence of any BSD users? We see 0 in the statistics we collect.

[drowe67]

Sorry we had an open PR with this notice that we forgot to merge: https://github.com/drowe67/LPCNet#status

[jg1uaa]

Do you have any evidence of any BSD users? We see 0 in the statistics we collect.

How about using Repology's packaing information? MacOS is kinda of BSD, MacPorts has freedv-gui ports.
I haven't heard that Freedv-GUI runs on other *BSDs yet, but FreeDV itself is ported for NetBSD ham/freedv and FreeBSD comms/freedv. I am an OpenBSD-7.6/amd64 user and I found this issue on this OS.

(out of topic: FreeBSD and DragonFlyBSD can buid socket.io-client-cpp and asio without problem so it might be easier running FreeBSD-GUI than NetBSD and OpenBSD.)

FreeDV-GUI has no LPCNet build option so I close this PR now, but please consider for non-linux hams.