[llvm] [WindowsDriver] Always consider `WinSdkVersion` (PR #130377)

[Fabrice de Gans via llvm-commits]

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@@ -444,6 +444,13 @@ bool getWindowsSDKDir(vfs::FileSystem &VFS, std::optional<StringRef> WinSdkDir,
     return !WindowsSDKLibVersion.empty();
   }
   if (Major == 10) {
+    if (WinSdkVersion) {
+      // Use the user-provided version as-is.
+      WindowsSDKIncludeVersion = WinSdkVersion->str();
+      WindowsSDKLibVersion = WindowsSDKIncludeVersion;
+      return true;
+    }
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Steelskin wrote:

The last SDK to support Windows XP was the Windows 7.1 SDK, for which the SDK version is not set because it is unused. By default, the latest Windows 7 SDK is installed at `C:\Program Files\Microsoft SDKs\Windows\v7.1` and that's just what `Path` is set to.

Windows 8 is a bit of a special case, where only the `Lib` directory has a versioned sub-directory set to either `win7`, `win8` or `winv6.3` (for Windows 8.1, counter-intuitively). The SDK installation only has one of these folders set up, which is a bit weird. Anyway, I *think* that linking against any of these library versions should work to make a Windows 7-compatible binary, assuming the app properly handles missing API calls.

I did not go back further but I think Windows SDK versioning was added in Windows 10 so there should not be any need to handle the argument elsewhere.

https://github.com/llvm/llvm-project/pull/130377