realpath issue with native[strict] symlinks

[Jeremy Drake]

> > Treating mapped/subst drives as though they were not symlinks, without
> > messing with intermedate symlinks.
>
> It was that simple, surprise, surprise...

It turns out it wasn't, after all.  This only seems to work at the root of
a subst-ed drive.  I just got the following error:
error: [Errno 2] No such file or directory:
'C:/msys32/home/Administrator/MINGW-packages/mingw-w64-python-sphinxcontrib-serializinghtml/pkg/mingw-w64-clang-aarch64-python-sphinxcontrib-serializinghtml/clangarm64/lib/python3.8/site-packages/sphinxcontrib/serializinghtml/locales/sphinxcontrib.serializinghtml.pot'

Where T:\ -> C:\msys32\home\Administrator\MINGW-packages and current
directory was under /t/

I was under the impression that that code iterated through path
components, so simply claiming that it wasn't a symlink when it got to the
"symlink" at the root of the drive would suffice, but apparently it's not
so simple.