FCS makes calls to kernel32.dll when running on OSX

[nosami]

https://github.com/fsharp/FSharp.Compiler.Service/blob/c1ca06144d8194000cf6b86f5f26bdc433ccaa7d/src/absil/ilread.fs#L169

[7sharp9]

Ive notices this a lot too, Its detrimental to performance on the x-plat compiler and tools.

[dsyme]

If possible please submit a PR to change this throw-and-catch to a conditional that detects whether we are running on Windows: https://github.com/fsharp/FSharp.Compiler.Service/blob/master/src/absil/ilread.fs#L3977