qmake does not find features file after setting QMAKEFEATURES

I have installed Qwt:

Code:

---

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

---

I set `QMAKEFEATURES` as according to the docs:

Code:

---

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

---

Sanity-check:

Code:

---

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

---

In my project .pro file I add qwt:

Code:

---

QT += qwt

---

When I build...

Code:

---

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

---

I have tried using an environment variable instead:

Code:

---

$ 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:

Code:

---

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

---

Same error again.

Why won't qmake pick up the prf file?

It should be:

Code:

---

CONFIG += qwt

---

Not

Code:

---

QT += qwt

---