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

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trcrsired wrote:

> @trcrsired I appreciate the response, but I'm not really willing to enter an ideological debate. I want to use what's practical, scalable, and supported.
> 
> You mentioned using Android to develop; this is very interesting, and there are still solutions. Have you considered getting a USB-C SD card reader and a small SD card (or hopefully you have a phone that still has a microSD slot), formatting that card as exFAT, and then installing your Windows SDK and VC tools there?
> 
> As for your diagram, there is separation but somehow I doubt it is to the extent that you claim. Many parts of the MSVC STL are developed _directly against ntdll_, such as `std::shared_mutex`. Some are developed against internal behaviours of UCRT. There is API separation but there is internal reliance on certain behaviour; that is why I said that.

SD card on android is another mess now. Android would automatically format your sd card if it is unformatted, plus nowadays all phones get rid of sdcard slots. In fact, apple is even trying to get rid of the last usb-c port in favor of magsafe.
https://9to5mac.com/2025/03/19/eu-confirms-apple-can-make-a-portless-iphone-without-usb-c/

Considering android vendors always tries to copy what apple does. Even the last usb-c port would be gone. So you cannot use small sdcard reader in the future i guess.

This is a perfect example why monopoly like apple and google make the entire things worse. And unfortunately, the US does not give a f on monopoly.

The criticism of Richard stallman to LLVM on "LLVM is a terrible setback" is exactly because of the reason like this. Google has been long time spreading misinformation on GPL-3.0 which prevents tiviozation.

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