[clang] [clang] Support --sysroot= for ${arch}-windows-msvc targets (PR #96417)

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Andarwinux wrote:

> I am not trying to argue what the license LLVM should choose. I am just trying to describe the consequence of what we get right now which is why you cannot do things like mount ntfs for example.

Yes. I added -Xmicrosoft-windows-sys-root, thinking it would be sufficient, but it turns out it's not. See https://github.com/mpv-player/mpv/pull/16750. The case conversion issue was one of the things I was having trouble with. Also, llvm-rc doesn't support winsysroot, so I had to force llvm-windres instead. sysroot will solve these problems in a way that's elegant for end users. (Though it's actually shifting all the complexity to sysroot generator)

> See that is the problem. Getting approval by google is exactly the issue. Google should not be the one who makes decisions on projects like LLVM.

You can't deny the existence of economics. Large companies like Google have indeed contributed the most to LLVM, which determines their dominance.

> You should not expect commercial companies to support their opponents' platforms. The community is more motivated than commercial companies to support this feature.

Just because Android and Windows are rivals doesn't mean Chromium is the same. Enterprises aren't monolithic.

Relying solely on the community is a dead end. Just look at GCC and MinGW. they've fallen on hard times precisely because of the lack of support form companies. For example, GCC still doesn't properly support AVX2/AVX512 on Windows, and MinGW still can't get rid of x87 FPU. These issues have existed for over a decade and remain unresolved. Enterprises won't use GCC, and the community has no incentive to fix them.



https://github.com/llvm/llvm-project/pull/96417