tests: C++ compilation test

This test includes one of wayland headers, which produced
error with C++ compiler. C compiler can't be used for this test,
because it issues only a warning[1] and only when wayland headers
are not installed in system headers path (/usr/include).

[1] wayland-server-protocol.h:201:2: warning: implicit declaration of function ‘wl_resource_post_event’

[daniels: Merged in Marek's follow-up to check for a C++ compiler.]

Signed-off-by: Mariusz Ceier <mceier+wayland@gmail.com>
Signed-off-by: Marek Chalupa <mchqwerty@gmail.com>
Reviewed-by: Daniel Stone <daniels@collabora.com>