Fixing binary reader on xplat

Author: ncave

src/absil/ilread.fs

@@ -3946,15 +3946,15 @@ let ClosePdbReader pdb =
 
 let OpenILModuleReader infile opts = 
 
-    if not runningOnMono then
+   try 
         let mmap = MemoryMappedFile.Create infile
         let modul,ilAssemblyRefs,pdb = genOpenBinaryReader infile mmap opts
         { modul = modul 
           ilAssemblyRefs=ilAssemblyRefs
           dispose = (fun () -> 
             mmap.Close()
             ClosePdbReader pdb) }
-    else
+    with _ ->
         let mc = ByteFile(infile |> FileSystem.ReadAllBytesShim)
         let modul,ilAssemblyRefs,pdb = genOpenBinaryReader infile mc opts
         { modul = modul 

src/fsharp/CompileOps.fs

@@ -2602,8 +2602,8 @@ type TcConfig private (data : TcConfigBuilder,validate:bool) =
                     clrRoot, (int v1, sprintf "v%d.%d" v1 v2), (v1=5us && v2=0us && v3=5us) // SL5 mscorlib is 5.0.5.0
                 | _ -> 
                     failwith (FSComp.SR.buildCouldNotReadVersionInfoFromMscorlib())
-            with _ -> 
-                error(Error(FSComp.SR.buildCannotReadAssembly(filename),rangeStartup))
+            with e ->
+                error(Error(FSComp.SR.buildErrorOpeningBinaryFile(filename, e.Message), rangeStartup))
         | _ ->
             None, MSBuildResolver.HighestInstalledNetFrameworkVersionMajorMinor(), false
 
@@ -2657,8 +2657,8 @@ type TcConfig private (data : TcConfigBuilder,validate:bool) =
                 checkFSharpBinaryCompatWithMscorlib filename ilReader.ILAssemblyRefs ilReader.ILModuleDef.ManifestOfAssembly.Version rangeStartup;
                 let fslibRoot = Path.GetDirectoryName(FileSystem.GetFullPathShim(filename))
                 fslibRoot (* , sprintf "v%d.%d" v1 v2 *)
-            with _ -> 
-                error(Error(FSComp.SR.buildCannotReadAssembly(filename),rangeStartup))
+            with e ->
+                error(Error(FSComp.SR.buildErrorOpeningBinaryFile(filename, e.Message), rangeStartup))
         | _ ->
             data.defaultFSharpBinariesDir