Fix Fcs/build when proto is built

[KevinRansom]

When running fcs/build.cmd and the proto compiler already exists the build fails with:

The issue is due to Directory.Build.Props and .targets automatically redirecting the compiler.

This is not desired behavior from fcs\build, whose job is to build and test the FSharp.Compiler.Service.dll

       "c:\kevinransom\visualfsharp\fcs\FSharp.Compiler.Service.sln" (Build target) (1:2) ->
       "c:\kevinransom\visualfsharp\fcs\FSharp.Compiler.Service.ProjectCrackerTool\FSharp.Compiler.Service.ProjectCrackerTool.fsproj" (default target) (5:10) ->
       "c:\kevinransom\visualfsharp\fcs\FSharp.Compiler.Service.ProjectCrackerTool\FSharp.Compiler.Service.ProjectCrackerTool.fsproj" (Build target) (5:11) ->
       (ResolveAssemblyReferences target) ->
         C:\Program Files\dotnet\sdk\3.0.100-preview3-010343\Microsoft.Common.CurrentVersion.targets(2114,5): warning MSB3277: Found conflicts between different versions of "Microsoft.Build.Framework" that could not be resolved.  These reference conflicts are listed in the build log when log verbosity is set to detailed. [c:\kevinransom\visualfsharp\fcs\FSharp.Compiler.Service.ProjectCrackerTool\FSharp.Compiler.Service.ProjectCrackerTool.fsproj]
         C:\Program Files\dotnet\sdk\3.0.100-preview3-010343\Microsoft.Common.CurrentVersion.targets(2114,5): warning MSB3277: Found conflicts between different versions of "Microsoft.Build.Engine" that could not be resolved.  These reference conflicts are listed in the build log when log verbosity is set to detailed. [c:\kevinransom\visualfsharp\fcs\FSharp.Compiler.Service.ProjectCrackerTool\FSharp.Compiler.Service.ProjectCrackerTool.fsproj]


       "c:\kevinransom\visualfsharp\fcs\FSharp.Compiler.Service.sln" (Build target) (1:2) ->
       "c:\kevinransom\visualfsharp\fcs\FSharp.Compiler.Service.ProjectCrackerTool\FSharp.Compiler.Service.ProjectCrackerTool.fsproj" (default target) (5:10) ->
       "c:\kevinransom\visualfsharp\fcs\FSharp.Compiler.Service.ProjectCrackerTool\FSharp.Compiler.Service.ProjectCrackerTool.fsproj" (Build target) (5:11) ->
       (CoreCompile target) ->
         c:\kevinransom\visualfsharp\artifacts\bin\FSharp.Build\Proto\net46\Microsoft.FSharp.Targets(277,9): error MSB6006: "dotnet.exe" exited with code 1. [c:\kevinransom\visualfsharp\fcs\FSharp.Compiler.Service.ProjectCrackerTool\FSharp.Compiler.Service.ProjectCrackerTool.fsproj]


       "c:\kevinransom\visualfsharp\fcs\FSharp.Compiler.Service.sln" (Build target) (1:2) ->
       "c:\kevinransom\visualfsharp\fcs\samples\EditorService\EditorService.fsproj" (default target) (9:14) ->
       "c:\kevinransom\visualfsharp\fcs\samples\EditorService\EditorService.fsproj" (Build target) (9:15) ->
       "c:\kevinransom\visualfsharp\fcs\FSharp.Compiler.Service\FSharp.Compiler.Service.fsproj" (default target) (13:29) ->
         c:\kevinransom\visualfsharp\artifacts\bin\FSharp.Build\Proto\net46\Microsoft.FSharp.Targets(277,9): error MSB6006: "dotnet.exe" exited with code 1. [c:\kevinransom\visualfsharp\fcs\FSharp.Compiler.Service\FSharp.Compiler.Service.fsproj]


       "c:\kevinransom\visualfsharp\fcs\FSharp.Compiler.Service.sln" (Build target) (1:2) ->
       "c:\kevinransom\visualfsharp\fcs\samples\EditorService\EditorService.fsproj" (default target) (9:14) ->
       "c:\kevinransom\visualfsharp\fcs\samples\EditorService\EditorService.fsproj" (Build target) (9:16) ->
       "c:\kevinransom\visualfsharp\fcs\FSharp.Compiler.Service\FSharp.Compiler.Service.fsproj" (default target) (13:31) ->
         c:\kevinransom\visualfsharp\artifacts\bin\FSharp.Build\Proto\net46\Microsoft.FSharp.Targets(277,9): error MSB6006: "dotnet.exe" exited with code 1. [c:\kevinransom\visualfsharp\fcs\FSharp.Compiler.Service\FSharp.Compiler.Service.fsproj]

    8 Warning(s)
    3 Error(s)

Time Elapsed 00:00:03.34
Running build failed.