Bug#1125598: amgcl: FTBFS with CMake 4.2

[Santiago Vila]

> For this particular package, I would try the attached patch.

Note: Didn't realize that the author already fixed this in exactly the same way:

https://github.com/ddemidov/amgcl/commit/93827a00fc926d951c75f08fdb1d491912ff7065

[ So, no need to contact them about this ]

Dima: I'm a team member. Would it help if I apply the patch, or would
you prefer to take care of this? (there is a new upstream 1.4.5 to
which you might want to upgrade).

Thanks.