fsc compilation fix

Since Fsc always skips the first argument, it is important to use a dummy argument when calling a Compile function. Otherwise, following compiler options can be ignored. For example, the current version of FAKE always ignores Output parameter, because "-o" is the first argument that appears in optsArr (thus, it is ignored along with the second argument that specifies the output file name). For your [reference](https://github.com/fsharp/FSharp.Compiler.Service/blob/6637eec059597667fa33038a3b65978d73d32624/tests/service/FscTests.fs#L127), Fsc compiler test code also includes "fsc.exe" as the first argument when calling the Compile function.
Can we put it without duplication on the line where the `Compile` get called?