Add basic fstat() support. Now all that is needed is to modify ALL of the file systems.

include/sys/stat.h

@@ -155,9 +155,7 @@ extern "C"
 int mkdir(FAR const char *pathname, mode_t mode);
 int mkfifo(FAR const char *pathname, mode_t mode);
 int stat(const char *path, FAR struct stat *buf);
-#if 0 /* Not yet supported */
 int fstat(int fd, FAR struct stat *buf);
-#endif
 
 #undef EXTERN
 #if defined(__cplusplus)