Indeed this was a bit strange, however I should be using standard build chain.
The warning was
"/qmlcalc-build-harmattan-Harmattan_Target_-_QEmu_PR1_2__Qt_SDK__Release/../qmlcalc/main.cpp:34: warning: the address of 'CalcEngine calcEng()' will always evaluate as 'true'"
coming from line
"rootContext->setContextProperty("calcOpEngine", &calcEng);",
didn't dig in but warning implies there's an evaluation on the pointer value.
I can of course remove the 0 argument if you prefer.

Details on my build environemnt:
Freshly installed Ubuntu 12.04 host with Mer platform SDK with Harmattan Qt SDK (https://wiki.merproject.org/wiki/Nemo/GettingStartedUsingQtSDK), QtCreator 2.4.1 from the Qt SDK.
Build setting is
"qmake: qmake qmlcalc.pro -r -spec linux-g++-maemo"
and the actual qmake:
"QMake version 2.01a
Using Qt version 4.8.1 in /usr/lib/x86_64-linux-gnu"