meson: fix build in freebsd
_XOPEN_SOURCE works differently on freebsd and breaks build
freebsd packaging already patches this out: https://github.com/freebsd/freebsd-ports/blob/main/graphics/libplacebo/files/patch-meson.build
_XOPEN_SOURCE works differently on freebsd and breaks build
freebsd packaging already patches this out: https://github.com/freebsd/freebsd-ports/blob/main/graphics/libplacebo/files/patch-meson.build
VideoLAN code repository instance