fix Windows build issue

[tigercosmos]

It is not able to build on Windows by following README.
As AppVeyor CI use VS 2015, it seems the script is designed for VS 2015.

I try three environment:

• Windows10 + VS2017

not work at the beginning

• Windows10 + VS1017 with 2015 tool

PR #18145 can solve download rustc problem, but build failed.

• Windows10 + VS2015

Work pretty well.

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• ./mach build -d does not report any errors
• ./mach test-tidy does not report any errors
• These changes fix #18055 (github issue number if applicable).

• There are tests for these changes OR
• These changes do not require tests because _____

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This change is 

[highfive]

Thanks for the pull request, and welcome! The Servo team is excited to review your changes, and you should hear from @cbrewster (or someone else) soon.

[atouchet]

Is #16307 an incomplete solution? I believe it should be possible to build with VS 2017.

[tigercosmos]

Yes, I think so. I tested in clean environment with windows10 and VS2017. Maybe need some package not mentioned in readme.

[jdm]

r? @larsberg

[atouchet]

@jdm I think you mean @larsbergstrom

[larsbergstrom]

Sorry for the delay on these! I will test these on Saturday.

I would expect Servo to build cleanly in VS2015 and VS2017, largely due to the work of @UK992. The main edge cases I'd expect are trying to build within a non-cmd.exe shell (powershell, cygwin, etc.) or with some more interesting environment variables set. I'll try to dig into what's going on this weekend when I have time to sit down with it. Sorry again for the delay!

[tigercosmos]

It's very weird. I try again on a new PC with VS2017 & Win10. No #18145 happens, and it works. I even not install 2015 tools. But this time I install many components (not just README mentioned). I guess some components are critical.

[larsbergstrom]

Yeah, I've confirmed on a clean machine & VM that VS 2017 is sufficient to build Servo, so I am closing this. I will look at the other issues you've raised now...

[tigercosmos]

@larsbergstrom Could you tell me which window10 version is used and what VS2017 components installed. I am still very confused, because in many times I have tried, I only success once, and I don't know why.

[larsbergstrom]

I'm on Windows 10 Home, version 1703, build 15063.540.

I installed Visual Studio 2017, custom installation adding Visual C++.