Bug#807318: libmpich-dev: should add Depends: to match hard-wired gcc dependency in mpicxx.h

[peter green]

>
> /usr/include/mpich/mpicxx.h has a hardwired dependency on the gcc used
> to build mpich (gcc 5.2):
>
> #ifdef __GNUC__
> # if __GNUC__>= 5
> #  if __GNUC_MINOR__>  2&&  2 == 2
> #  error 'Please use the same version of GCC and g++ for compiling MPICH and user MPI programs'
> #  endif
> # endif
> #endif
>
> But the current gcc (on s390x) is 5.3.  So an error is thrown when
> building client programs (cf. Bug#803477), making mpich mostly
> unusable on this architecture.
>    
I wonder if this logic needs to be changed since gcc changed it's 
version numbering. As I understand it with 5.x and up the second digit 
is being used in the way the third digit used to be used.