Regression: can no longer shadow-build Qt on Windows from symlinked network share directory

Starting with Qt 5.8.0, it is no longer possible to do a Qt shadow-build on Windows from a symlinked network shared directory.

Formerly, I could do a "mklink /d" to a network share directory (mapped to a drive letter), then invoke configure from a different directory on the filesystem (via relative path) for a shadow build, allowing me to have multiple Parallels VMs for different platforms that share the same source (via shared directory), with the build for the platform residing on the VM filesystem.

Now, the build failure occurs because $$shadowed($$PWD) doesn't work: the $$shadowed call resolves to no prefix in this case.

As a result, I'm forced to keep a copy of the source on my Windows VMs, which must be synced through robocopy for uncommitted changes, which is a time and space consuming step that is easy to forget.