In Cwd.xs, tidy the conditional code related to symlinks.

In Cwd.xs, tidy the conditional code related to symlinks.

Move the variable symlink inside the conditionally compiled code, to avoid
on platforms which don't have symlinks about an unused variable.
Move the pre-processor directives back to column zero - they were indented as
part of the upgrade to PathTools 3.26_01 in c7304ea2604337d2.
Correct the indentation of some lines [always just a closing '}'], which was
making the code harder to follow. All these lines seem to have been left
unaltered by c7304ea2604337d2, when code surrounding them changed.