The F# compiler automatically generates assembly for some non-standard runtime (such as Silverlight or Compact Framework) if you reference the appropriate (non-standard) version of the mscorlib.dll and FSharp.Core.dll assemblies in your F# project. The Silverlight version of the assemblies can be found here (on my machine):
  C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\Silverlight\v3.0\mscorlib.dll
  C:\Programs\Development\FSharp-1.9.9.9\Silverlight\2.0\bin\FSharp.Core.dll
This is a more user-friendly replacement for the --noframework and --cli-root parameters mentioned in the question referenced by Pretzel.