MSVC: Improve MSVC support (part 3)

[echoix]

Replaces #356, named "Msvc support 3"

I rebased/cherry-picked the PR #356 in order to make it reviewable. The last 10 commits of that PR were of interest, but multiple have already been included, so less remains.

I tried to make it such as it highlights what was different in the cases where conflicts existed. This means that not everything from this PR might be worthy of including it. At least it is reviewable, and mergeable.

While rebasing, I had to solve the conflict where I think there had been a bad resolution in #3621, and here it contains what I think the original commit wanted to do. See https://github.com/OSGeo/grass/pull/356#discussion_r2030231408 and https://github.com/OSGeo/grass/pull/356#discussion_r2030234802.