Qmake does not find features file after setting QMAKEFEATURES

[jmalicke]

I have installed Qwt:

@/usr/local/qwt-6.1.0/
features/
qwt.prf
qwtconfig.pri
qwtfunctions.pri@

I set QMAKEFEATURES as according to the docs:

@qmake -set QMAKEFEATURES /usr/local/qwt-6.1.0/features@

Sanity-check:

@$ qmake -query
QMAKEFEATURES:/usr/local/qwt-6.1.0/features
...@

In my project .pro file I add qwt:

@QT += qwt@

When I build...

@$ qmake
$ make
...
Project ERROR: Unknown module(s) in QT: qwt@

I have tried using an environment variable instead:

@$ export QMAKEFEATURES=/usr/local/qwt-6.1.0/features
$ echo ${QMAKEFEATURES}
/usr/local/qwt-6.1.0/features/
$ qmake
$ make@

And I still get the same problem.

I have tried to direct include the .prf in the .pro file:

@include ( /usr/local/qwt-6.1.0/features/qwt.prf )@

Same error.

Why won't qmake pick up the prf file?