[xharness] Add project configurations to run & debug Makefile generation. (#4739)

This also required a minor fix to allow relative directories as the root
directory.

tests/xharness/Harness.cs

@@ -194,7 +194,7 @@ namespace xharness
 		void LoadConfig ()
 		{
 			ParseConfigFiles ();
-			var src_root = Path.GetDirectoryName (RootDirectory);
+			var src_root = Path.GetDirectoryName (Path.GetFullPath (RootDirectory));
 			MONO_PATH = Path.GetFullPath (Path.Combine (src_root, "external", "mono"));
 			WATCH_MONO_PATH = make_config ["WATCH_MONO_PATH"];
 			TVOS_MONO_PATH = MONO_PATH;

tests/xharness/xharness.csproj

@@ -45,6 +45,14 @@
       <Variable name="MONO_ENV_OPTIONS" value="--trace=E:all" />
     </EnvironmentVariables>
   </PropertyGroup>
+  <PropertyGroup Condition=" '$(RunConfiguration)' == 'Makefile.inc' ">
+    <StartAction>Project</StartAction>
+    <StartArguments>--configure --autoconf --rootdir ..</StartArguments>
+  </PropertyGroup>
+  <PropertyGroup Condition=" '$(RunConfiguration)' == 'Makefile-mac.inc' ">
+    <StartAction>Project</StartAction>
+    <StartArguments>--configure --autoconf --rootdir .. --mac </StartArguments>
+  </PropertyGroup>
   <ItemGroup>
     <Reference Include="System" />
     <Reference Include="System.Xml" />