squash! mingw: lstat: compute correct size for symlinks

Move this, and "fscache: compute correct symlink size in `lstat()`",
into "kblees/kb/symlinks".

Maybe even squash it into the appropriate commits, e.g. "mingw: teach
fscache and dirent about symlinks"?

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho