Enable std::filesystem on libc++ on Windows

tor-browser!829 (closed) could use std::filesystem to avoid us using Win32 APIs with all their shenanigans.

Currently, we don't have it on Windows because Mozilla used to disable it.

In 116, they had to enable it because of LLVM updates (fstream now requires std::filesystem, in LLVM's implementation).

Tom said we can take that change already.

added 13.5 stable Build System Next Windows labels

assigned to @pierov

removed Next label

added Doing label

mentioned in merge request !851 (merged)

added Needs Review label and removed Doing label

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added Backport Next labels

marked this issue as related to #41021 (closed)

marked this issue as related to #41022 (closed)

marked this issue as related to #41028 (closed)

marked this issue as related to #41029 (closed)

mentioned in merge request tor-browser!860 (merged)

marked this issue as related to tor-browser#42163 (closed)

@richard since we're not backporting tor-browser!860 (merged), do we still want to Backport this?

It wouldn't be required anymore, but if we took !851 (merged) (this + #41016 (closed)) we would have the same toolchain for 13.0 and 13.5 again (so, consistency).

I don't see a compelling reason to backport this to stable.

Consistency, especially if we end up taking #41016 (closed).

marked this issue as related to #41033 (closed)

marked this issue as related to #41034 (closed)

removed the relation with #41028 (closed)

removed the relation with #41029 (closed)

removed Backport label