Fix how we detect where link.exe is

[MichalStrehovsky]

Seems like when the Visual C++ workload is not installed in VS, we get a useless build error:

         "C:\Users\[redacted]\.nuget\packages\microsoft.dotnet.ilcompiler\1.0.0-alpha-28504-01\build\findvcvarsall.bat" amd64
         INFO: Could not find files for the given pattern(s).
         C:\Program Files (x86)\Windows Kits\NETFXSDK\4.6.1\lib\um\x64;C:\Program Files (x86)\Windows Kits\10\lib\10.0.18362.0\ucrt\x64;C:\Program Files (x86)\Windows Kits\10\lib\10.0.18362.0\um\x64;C:\Program Files (x86)\Windows Kits\NETFXSDK\4.8\lib\um\x64;C:\Program Files (x86)\Windows Kits\10\lib\10.0.18362.0\ucrt\x64;C:\Program Files (x86)\Windows Kits\10\lib\10.0.18362.0\um\x64;
       Done executing task "Exec".
     1>C:\Users\[redacted]\.nuget\packages\microsoft.dotnet.ilcompiler\1.0.0-alpha-28504-01\build\Microsoft.NETCore.Native.Windows.props(98,43): error MSB4184: The expression ""System.String[]".GetValue(1)" cannot be evaluated. Index was outside the bounds of the array.

[woachk]

Hello,

Could LLVM and MinGW be used from https://github.com/mstorsjo/llvm-mingw for example to not need VS and the Windows SDK installed?

Ideally, only needed things the LLVM lld linker and the .lib files, without having to ship a whole MSVC toolchain.

LLVM-MinGW would allow to cross-compile builds to Windows from Linux or macOS too in an easy to set up way.

I'd also try the LLD link.exe compatible frontend...

Thanks,