Created Unassigned: Compile errors in stat.h if /Zc:wchar_t is enabled [10601]

There are compile errors when including vld.h in a project with /Zc:wchar_t enabled:
```
Severity Code Description Project File Line Suppression State
Error C2061 syntax error: identifier '_dev_t' asyncserverc C:\Program Files (x86)\Windows Kits\10\Include\10.0.10586.0\ucrt\sys\stat.h 29
Error C2061 syntax error: identifier 'st_ino' asyncserverc C:\Program Files (x86)\Windows Kits\10\Include\10.0.10586.0\ucrt\sys\stat.h 30
Error C2059 syntax error: ';' asyncserverc C:\Program Files (x86)\Windows Kits\10\Include\10.0.10586.0\ucrt\sys\stat.h 30
Error C2061 syntax error: identifier 'st_rdev' asyncserverc C:\Program Files (x86)\Windows Kits\10\Include\10.0.10586.0\ucrt\sys\stat.h 35
...
```

The include of wchar.h in file vld_def.h should be changed as follows:

```
#ifndef _WCHAR_T_DEFINED
# include <wchar.h>
#endif /* _WCHAR_T_DEFINED */
```