tests: allow cross-compiling the tests
I am trying to cross-compile from macOS for FreeBSD and this is currently failing since the tests attempt to build a native binary that links against the wayland-client and wayland-server libraries for the FreeBSD system. I believe we should be building them for the target system and not the current host (especially since there is no way to build wayland-client and wayland-server for macOS, but I do want to check that the files build correctly for FreeBSD).
Signed-off-by: Alex Richardson Alexander.Richardson@cl.cam.ac.uk