Port Roslyn Common Props change to 2.0.0

Author: wtgodbe

tests/dir.props

@@ -1,3 +1,4 @@
+<?xml version="1.0" encoding="utf-8"?>
 <Project ToolsVersion="12.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
   <!--
     $(OS) is set to Unix/Windows_NT. This comes from an environment variable on Windows and MSBuild on Unix.
@@ -64,6 +65,11 @@
   <!-- Provides properties for dependency versions and configures dependency verification/auto-upgrade. -->
   <Import Project="$(ProjectDir)..\dependencies.props" />
 
+  <!-- Use Roslyn Compilers to build -->
+  <Import Project="$(RoslynPropsFile)" Condition="'$(RunningOnUnix)'!='true' and Exists('$(RoslynPropsFile)') and '$(UseRoslynCompilers)'!='false'" />
+  <Import Project="$(RoslynPropsFile)" Condition="'$(RunningOnUnix)'=='true' and Exists('$(RoslynPropsFile)')" />
+
+
    <ItemGroup> 
      <!-- Need to escape double forward slash (%2F) or MSBuild will normalize to one slash on Unix. -->
      <DotnetSourceList Include="$(PackagesDir)AzureTransfer\" Condition="'$(OverwriteCoreClrPackageVersion)' == 'true'" />