[Pyrex] __Pyx_ImportModule defined twice

[Stefan Behnel]

Stefan Behnel wrote:
> using cimports with the generated *_api.h file can create multiple definitions
> of __Pyx_ImportModule(), so it should be wrapped by a
> 
> #ifndef __PYX_HAVE_RT_ImportModule
> #define __PYX_HAVE_RT_ImportModule
> ...
> #endif

BTW, the same problem arises in C code that uses two different Cython APIs, so
the above is actually required anyway.

Stefan