os: make Stat work on FAT file system

It appears calling GetFileInformationByHandleEx with
FILE_ATTRIBUTE_TAG_INFO fails on FAT file system. FAT does not
support symlinks, so assume there are no symlnks when
GetFileInformationByHandleEx returns ERROR_INVALID_PARAMETER.

Fixes #29214

Change-Id: If2d9f3288bd99637681ab5fd4e4581c77b578a69
Reviewed-on: https://go-review.googlesource.com/c/154377
Run-TryBot: Alex Brainman <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>

Author: alexbrainman

src/os/types_windows.go

@@ -51,7 +51,15 @@ func newFileStatFromGetFileInformationByHandle(path string, h syscall.Handle) (f
 	var ti windows.FILE_ATTRIBUTE_TAG_INFO
 	err = windows.GetFileInformationByHandleEx(h, windows.FileAttributeTagInfo, (*byte)(unsafe.Pointer(&ti)), uint32(unsafe.Sizeof(ti)))
 	if err != nil {
-		return nil, &PathError{"GetFileInformationByHandleEx", path, err}
+		if errno, ok := err.(syscall.Errno); ok && errno == windows.ERROR_INVALID_PARAMETER {
+			// It appears calling GetFileInformationByHandleEx with
+			// FILE_ATTRIBUTE_TAG_INFO fails on FAT file system with
+			// ERROR_INVALID_PARAMETER. Clear ti.ReparseTag in that
+			// instance to indicate no symlinks are possible.
+			ti.ReparseTag = 0
+		} else {
+			return nil, &PathError{"GetFileInformationByHandleEx", path, err}
+		}
 	}
 
 	return &fileStat{