Implement FileSystem::GetPermissions for Windows.

[amccarth]

Summary

I'm working on loading Windows mini dumps (like Linux core files). I'm doing this change as a separate PATCH in order to break the work into digestible chunks.

The core-loading code calls FileSpec::Readable (twice!) before attempting to open the file, so we need GetPermissions to indicate whether the user can read the file.

[chaoren]

Looks good.

[amccarth]

http://reviews.llvm.org/rL242568

source/Host/windows/FileSystem.cpp

 //===-- FileSystem.cpp ------------------------------------------*- C++ -*-===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
 #include "lldb/Host/windows/windows.h"
 
 #include <shellapi.h>
+#include <sys/stat.h>
+#include <sys/types.h>
 
 #include "lldb/Host/FileSystem.h"
 #include "llvm/Support/FileSystem.h"
 
 using namespace lldb_private;
 
 FileSpec::PathSyntax
 FileSystem::GetNativePathSyntax()
FileSystem::DeleteDirectory(const FileSpec &file_spec, bool recurse)
     }
     return error;
 }
 
 Error
 FileSystem::GetFilePermissions(const FileSpec &file_spec, uint32_t &file_permissions)
 {
     Error error;
-    error.SetErrorStringWithFormat("%s is not supported on this host", __PRETTY_FUNCTION__);
+    // Beware that Windows's permission model is different from Unix's, and it's
+    // not clear if this API is supposed to check ACLs.  To match the caller's
+    // expectations as closely as possible, we'll use Microsoft's _stat, which
+    // attempts to emulate POSIX stat.  This should be good enough for basic
+    // checks like FileSpec::Readable.
+    struct _stat file_stats;
+    if (::_stat(file_spec.GetCString(), &file_stats) == 0)
+    {
+        // The owner permission bits in "st_mode" currently match the definitions
+        // for the owner file mode bits.
+        file_permissions = file_stats.st_mode & (_S_IREAD | _S_IWRITE | _S_IEXEC);
+    }
+    else
+    {
+        error.SetErrorToErrno();
+    }
+
     return error;
 }
 
 Error
 FileSystem::SetFilePermissions(const FileSpec &file_spec, uint32_t file_permissions)
 {
     Error error;
     error.SetErrorStringWithFormat("%s is not supported on this host", __PRETTY_FUNCTION__);