petsc 3.15 merged VecScatter into PetscSF

[minrk]

Private variables like _p_VecScatter were removed.

I'm not sure if there's a better way to get at this without private APIs, because public names like VecScatter work fine as aliases to the new type

testing in conda-forge/daetk-feedstock#6

[minrk]

the conda-forge build with this patch succeeded

[jedbrown]

I'm curious why daetk uses pointers to the private names as in

daetk/DaetkPetscVec.h

Line 286 in 66b2a69

Petsc::cc::_p_VecScatter* my_gtol_;

rather than the public typedefs.

[minrk]

I've no idea! This was just the smallest patch I could come up with to get it building.

Presumably better to use public symbols, if possible.

Maybe just duplicating the original private typedefs, rather than importing them.

[cekees]

@minrk and @jedbrown, thanks. I have to admit that I don't remember why the pointers to private names came in here. It was before we moved to git, and I'd have to dig into the svn history. I believe that I can use the public typedefs now. Some of the complication here came from a long time ago where I was having some trouble with C++/C coupling. The coupling was done before PETSc had a C++ interface and when C++ compilers were all over the place in supporting standards. I've raised an issue (#11) but am just going to merge this to fix the compilation problems until I can go through carefully and clean this up.