Qt build problems after bump to 5.12.7

[John Soo]

Hi Guix,

I was looking into the failing freecad build and I found the following
bug from the qt 5.12.7 known bugs page
(https://wiki.qt.io/Qt_5.12.7_Known_Issues).

- Qt-based CMake projects might fail if their build directories contain dots:

  https://bugreports.qt.io/browse/QTBUG-81715

I think this probably effects more cmake based qt projects than just freecad.
The qt-build-system is based on cmake and many of the store paths and
build paths include semver version numbers.

What should we do?

Thanks,

John