Build fails with msbuild 15

[ghost]

Build fails with msbuild 15 on Arch Linux, with and error message about "/usr/lib/mono/msbuild/15.0/bin/Roslyn/Microsoft.CSharp.Core.targets" not being found

Project "/home/user/godot/modules/mono/editor/GodotSharpTools/GodotSharpTools.sln" on node 1 (default targets).
ValidateSolutionConfiguration:
  Building solution configuration "Release|Any CPU".
Project "/home/user/godot/modules/mono/editor/GodotSharpTools/GodotSharpTools.sln" (1) is building "/home/user/godot/modules/mono/editor/GodotSharpTools/GodotSharpTools.csproj" (2) on node 1 (default targets).
/usr/lib/mono/msbuild/15.0/bin/Microsoft.CSharp.CurrentVersion.targets(331,5): error MSB4019: The imported project "/usr/lib/mono/msbuild/15.0/bin/Roslyn/Microsoft.CSharp.Core.targets" was not found. Confirm that the path in the <Import> declaration is correct, and that the file exists on disk. [/home/user/godot/modules/mono/editor/GodotSharpTools/GodotSharpTools.csproj]
Done Building Project "/home/user/godot/modules/mono/editor/GodotSharpTools/GodotSharpTools.csproj" (default targets) -- FAILED.
Done Building Project "/home/user/godot/modules/mono/editor/GodotSharpTools/GodotSharpTools.sln" (default targets) -- FAILED.

Build FAILED.

"/home/user/godot/modules/mono/editor/GodotSharpTools/GodotSharpTools.sln" (default target) (1) ->
"/home/user/godot/modules/mono/editor/GodotSharpTools/GodotSharpTools.csproj" (default target) (2) ->
  /usr/lib/mono/msbuild/15.0/bin/Microsoft.CSharp.CurrentVersion.targets(331,5): error MSB4019: The imported project "/usr/lib/mono/msbuild/15.0/bin/Roslyn/Microsoft.CSharp.Core.targets" was not found. Confirm that the path in the <Import> declaration is correct, and that the file exists on disk. [/home/user/godot/modules/mono/editor/GodotSharpTools/GodotSharpTools.csproj]

    0 Warning(s)
    1 Error(s)

[ghost]

To clarify, this happens with Xamarin's msbuild. Microsoft's msbuild works fine.

[ryukinix]

@tagcup I got the same error on Rider IDE of Intellij IDEA. I'll try change the msbuild. EDIT: this fixed, but now I have another problem which complains about "'Fsharp' load finished with warnings: The reference assemblies for framework ".NETFramework,Version=v4.5""