Changed conditional from mono check to Windows

Author: nosami

src/absil/il.fs

@@ -13,11 +13,17 @@ open Microsoft.FSharp.Compiler.AbstractIL
 open Microsoft.FSharp.Compiler.AbstractIL.Internal
 open Microsoft.FSharp.Compiler.AbstractIL.Internal.Library
 open Microsoft.FSharp.Compiler.AbstractIL.Diagnostics
+open System
 open System.Collections.Generic
 open System.Collections
 
 let logging = false 
 
+let runningOnWindows =
+    match System.Environment.OSVersion.Platform with
+    | PlatformID.Win32NT | PlatformID.Win32S | PlatformID.Win32Windows | PlatformID.WinCE -> true
+    | _  -> false
+
 // Officially supported way to detect if we are running on Mono.
 // See http://www.mono-project.com/FAQ:_Technical
 // "How can I detect if am running in Mono?" section

src/absil/il.fsi

@@ -2275,6 +2275,7 @@ type ILPropertyRef =
      member Name: string
      interface System.IComparable
 
+val runningOnWindows: bool
 val runningOnMono: bool
 
 type ILReferences = 

src/absil/ilread.fs

@@ -3971,7 +3971,7 @@ let ClosePdbReader pdb =
 #endif
 
 let OpenILModuleReader infile opts = 
-    if not IL.runningOnMono then
+    if IL.runningOnWindows then
         let mmap = MemoryMappedFile.Create infile
         let modul,ilAssemblyRefs,pdb = genOpenBinaryReader infile mmap opts
         { modul = modul;