MAINT: SuperLU upstream fix for compile warnings

[alugowski]

Reference issue

Closes #19767

What does this implement/fix?

Fixes build warnings by bringing in the fix from upstream: xiaoyeli/superlu#128

[tylerjereddy]

While the patch is clearly small and seems safe enough, I would point out that we usually separate the application of individual SuperLU patches to a file scipy/sparse/linalg/_dsolve/SuperLU/scipychanges.patch.

Presumably this serves a few purposes, but the obvious is just organizational. While it is probably far more important to use that file for patches that have not yet been upstreamed, it may still make sense to use it here so that we're clear that we haven't updated to latest version again, just applied an individual patch.

There's some more recent discussion here: #19284. I'm not necessarily trying to block this PR though, just want whoever decides to merge to have this in mind.

[rgommers]

Since it's already fixed upstream, let's not bother with the patch file. We'll definitely pull in the fix next time we update SuperLU, so it'd only be extra work to remove the patch from the patch file at that point.

Thanks @alugowski for doing this, and thanks @tylerjereddy for the review.