How do I add options to the compiler/linker using the Qt IDE?
By adding apppropriate entries in the .pro file:
"QMAKE_CXXFLAGS":http://qt-project.org/doc/qt-5.0/qtdoc/qmake-variable-reference.html#qmake-cxxflags and "QMAKE_LFLAGS":http://qt-project.org/doc/qt-5.0/qtdoc/qmake-variable-reference.html#qmake-lflags
There are also variables for different configs like release, debug, shared lib, console etc.
Also there are some portable options for things like linking libraries (LIBS), setting additional include paths (INCLUDEPATH), defining symbols (DEFINES) etc.
Take a look at the list in the links above.