spatialaudio>zita-convolver compatibility on Windows

[MyunginLee]

I found that zita-convolver contains some unix compatible libraries which are conflicting in Windows machines. If we are trying to use windows for new 2809 machines or further windows installation with spatialaudio, we may have to make this part compatible.

#include <unistd.h>
https://stackoverflow.com/questions/22705751/cannot-open-include-file-unistd-h-no-such-file-or-directory

pthread.h
https://learn.microsoft.com/en-us/answers/questions/76739/fatal-error-c1083-cannot-open-include-file-39pthre.html

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