GenerateMSBuildEditorConfig task breaks incremental build on Windows when using different casing paths

**Version Used**: 17.10.4+10fbfbf2e

**Steps to Reproduce**:

1. Have a dummy under X\x.csproj (sdk)
2. Build from some y\dirs.proj with ProjectReference="..\X\x.csproj" -> full build
3. Build from another z\dirs.proj with ProjectReference=..\x\x.csproj" -> will trigger full build because path is invoked with lower case "x\"

**Diagnostic Id**:
Using "GenerateMSBuildEditorConfig" task from assembly "Current\bin\Roslyn\Microsoft.Build.Tasks.CodeAnalysis.dll"

Input file "x\obj\amd64\LegacyUri.UnitTests.Core.GeneratedMSBuildEditorConfig.editorconfig" is newer than output file

**Expected Behavior**:
No recompilton CoreCompile should happen on Windows because the paths are identical, just casing is different.