libmirserver.so and libmirclient.so both have symbols for mir_egl_mesa_display_is_valid()

mir_egl_mesa_display_is_valid() was originally made for Mesa to authenticate the EGLNativeDisplayType that it gets on the client side with the Mir server. However, since we started having internal clients, this symbol was added to libmirserver.so so our internal clients can authenticate their connection as well. (i'm guessing that this is because it was easier to do without changing mesa)

This is a problem because if an ipc client links to the libmirserver.so implementation of mir_egl_mesa_display_is_valid() (or vice versa), it will run code that doesn't make sense for the type of client that it is.
This might cause some funny bugs based on linking.