[CMake] Ninja and *.i targets

[Óscar Fuentes]

With the `Unix Makefiles' generator, a foo.i target is generated for
foo.cpp. That's very convenient. However, ninja doesn't list such
targets under `ninja help' and `ninja foo.i' complains about unknown
target.

Is this feature missing from the ninja generator? Is it because is hard
to implement or just lack of time?

I'm using cmake 2.8.9 and ninja 1.0.0 on Linux.