Proper executable check on Unix

[evgTSV]

Closes #840

Unfortunately, I haven't found ready-made solutions that are compatible with netstandard 2.0 and SDK project.

It perfectly works with Linux systems (tested on WSL and github runners). But the LStat function return -1 on MacOS for dotnet file, for directories it works.

Here are logs for MacOS:

[stdout]: MSBuild version 17.14.21+8929ca9e3 for .NET
  11:25:43 [DBG]  [stdout]:   Determining projects to restore...
  11:25:43 [DBG]  [stdout]:   Restored /var/folders/q0/wmf37v850txck86cpnvwm_zw0000gn/T/otavwa4j.mhn/SimpleNetfxLibrary/SimpleNetfxLibrary.ceproj (in 2.06 sec).
  11:25:43 [DBG]  [stdout]:   Determining projects to restore...
  11:25:43 [DBG]  [stdout]:   All projects are up-to-date for restore.
  11:25:43 [DBG]  [stdout]: Loading file: /private/var/folders/q0/wmf37v850txck86cpnvwm_zw0000gn/T/otavwa4j.mhn/SimpleNetfxLibrary/dotnet
  11:25:43 [DBG]  [stdout]: LStat returned -1
  11:25:43 [DBG]  [stdout]: UnixFileInfo has thrown: lstat failed for /private/var/folders/q0/wmf37v850txck86cpnvwm_zw0000gn/T/otavwa4j.mhn/SimpleNetfxLibrary/dotnet with error 0
  11:25:43 [DBG]  [stdout]: Loading file: /Users/runner/.dotnet
  11:25:43 [DBG]  [stdout]: LStat returned 0
  11:25:43 [DBG]  [stdout]: File type: 16384
  11:25:43 [DBG]  [stdout]: File: OtherExecute, OtherRead, GroupExecute, GroupRead, UserExecute, UserWrite, UserRead (493) IsDir: True

[ForNeVeR]

Thanks! I believe this is a step in the right direction.

[ForNeVeR]

I am concerned with the use of this library. As it looks to me, it's some undocumented implementation detail of the .NET runtime, right? Can we rely on libc instead?

[evgTSV]

Of course, but we need processing Stat call manually. In runtime source I've found how I need to impl this. I try to impl this.

[evgTSV]

Here is implementation of call from the runtime sources: https://github.com/dotnet/runtime/blob/5a4b89cc8dc951b12c3a40bb343aac44f32fd040/src/native/libs/System.Native/pal_io.c#L234

[evgTSV]

Okay, It sill dosen't work with MacOS. It works with only directories, on files it crashes. Maybe is error in the tests or in invalid path?

[evgTSV]

That is works with File.GetUnixFileMode()

[ForNeVeR]

Thank you so much!