Compressonator doesn't build on *BSD

[StanleySweet]

Possible workaround (not a proper fix) by @seragh here https://gitea.wildfiregames.com/Stan/0ad/src/commit/4d0fc39ba0d1677c9e4c3257bd7a045b0dcd577d/libraries/source/compressonator/patches/disable-sse.patch

[seragh]

A comment or two,

NULL is defined as nullptr, so no implicit conversion to bool or whatever on FreeBSD. Then <experimental/filesystem> unlike <filesystem> was missing, just that the c++17 version of that code doesn't build on Linux either, so choose the c++11 one to get something usable quickly.

Edit: add code tags so markup render doesn't eat includes