Windows build is broken out of the box

[papeh]

Describe the bug

Building the project using the instructions in README.md fails on a fresh clone on Windows using Visual Studio 2019

To Reproduce

• Clone the project
• Open x64_x86 Cross Tools Command Prompt for VS 2019 and cd to the repository root
• Run msbuild /t:Test build/icu-dotnet.proj Expected: project builds and tests pass Actual: build fails with

  "C:\fwrepo\icu-dotnet\build\icu-dotnet.proj" (Test target) (1) ->
  "C:\fwrepo\icu-dotnet\source\icu.net.sln" (Rebuild target) (3) ->
  (ValidateSolutionConfiguration target) ->
  C:\fwrepo\icu-dotnet\source\icu.net.sln.metaproj : error MSB4126: The specified solution configuration "Release|x86"
  is invalid. Please specify a valid solution configuration using the Configuration and Platform properties (e.g. MSBuild
  .exe Solution.sln /p:Configuration=Debug /p:Platform="Any CPU") or leave those properties blank to use the default solu
  tion configuration. [C:\fwrepo\icu-dotnet\source\icu.net.sln]

[ermshiperete]

It works with the "x64 Native Tools Command Prompt for VS 2019". With "x64_x86 Cross Tools Command Prompt for VS 2019" you can pass /p:Platform="Any CPU" and get a successful build (although some .NET Core 3.1 tests will still fail).

[ermshiperete]

161 contains a fix that makes the instructions from the README.md work again :smiley:

[papeh]

Solved now that we're building with dotnet