Add dependence for a cython file 

Sometimes we use some tool like autopxd to generate .pxd from .h . How can we add 

```cmake
cython_transpile(<pyx_file>
                 [LANGUAGE C | CXX]
                 [CYTHON_ARGS <args> ...]
                 [OUTPUT <OutputFile>]
                 [OUTPUT_VARIABLE <OutputVariable>]
                 DEPENDS XXX_pxd
                 )
add_custom_target(XXX_pxd)
```