Confusing error message: Could not find qmake configuration directory

If the environment variable QMAKESPEC is not defined, the following messages are displayed after saving a .pro file

C:/bash/local/qhull/qtpro/qhulllib.pro(0):Could not find qmake configuration directory
C:/bash/local/qhull/qtpro/qhulllib.pro(0):Could not find qmake configuration file

It took reading the Qt Creator code to figure out the cause.

"qmake configuration directory" – Environment variable QMAKESPEC was not defined
"qmake configuration file" – QMAKESPEC does not refer to a mkspecs directory (i.e., a directory containing 'qmake.conf').

I may have backed into this problem since my setup was unusual.

1) Install DevStudio binary version
2) make cleandist
3) build with mingw