Make the obvious Windows-only tools fail explicitly off the supported platform

src/app/Fake.DotNet.FxCop/FxCop.fs

@@ -226,4 +226,6 @@ let run param (assemblies : string seq) =
         composeCommandLine param assemblies
         |> Proc.run
         |> failAsrequired param
-        __.MarkSuccess()
+        __.MarkSuccess()
+    else
+        raise <| NotSupportedException("FxCop is currently not supported on mono")

src/app/Fake.DotNet.ILMerge/ILMerge.fs

@@ -179,4 +179,6 @@ let run parameters outputFile primaryAssembly =
         if 0 <> run.ExitCode then
             let args = getArguments outputFile primaryAssembly parameters
             failwithf "'ILMerge %s' failed." (String.separated " " args)
-        __.MarkSuccess()
+        __.MarkSuccess()
+    else
+        raise <| NotSupportedException("ILMerge is currently not supported on mono")

src/test/Fake.Core.UnitTests/Fake.DotNet.FxCop.fs

@@ -313,7 +313,15 @@ let testCases =
                              printfn "Unexpected failure %A level=%d index=%d" x level
                                  mapIndex
                              reraise()) ]
-    else []
+    else
+        [ testCase "Test failure on non-Windows platforms" <| fun _ ->
+              let p = FxCop.Params.Create()
+              Expect.throwsC (fun () -> FxCop.run p [])
+                  (fun ex ->
+                  Expect.equal (ex.GetType()) typeof<NotSupportedException>
+                      "Exception type should be as expected"
+                  Expect.equal ex.Message "FxCop is currently not supported on mono"
+                      "Exception message should be as expected") ]
 
 [<Tests>]
-let tests = testList "Fake.DotNet.FxCop.Tests" testCases
+let tests = testList "Fake.DotNet.FxCop.Tests" testCases

src/test/Fake.Core.UnitTests/Fake.DotNet.ILMerge.fs

@@ -207,7 +207,17 @@ let testCases =
                                   libs |> Seq.head
                                   libs |> Seq.last ]
                   "Strings should be assigned as expected" ]
-    else []
+    else
+        [ testCase "Test failure on non-Windows platforms" <| fun _ ->
+              let p = ILMerge.Params.Create()
+              let dummy = Guid.NewGuid().ToString()
+              let dummy2 = Guid.NewGuid().ToString()
+              Expect.throwsC (fun () -> ILMerge.run p dummy dummy2)
+                  (fun ex ->
+                  Expect.equal (ex.GetType()) typeof<NotSupportedException>
+                      "Exception type should be as expected"
+                  Expect.equal ex.Message "ILMerge is currently not supported on mono"
+                      "Exception message should be as expected") ]
 
 [<Tests>]
-let tests = testList "Fake.DotNet.ILMerge.Tests" testCases
+let tests = testList "Fake.DotNet.ILMerge.Tests" testCases