on Linux, qt 4.0 and flite are apparently required by default but not checked for, the dependencies have to be satisfied manually, because there is no check done prior to the build process that informs the user that dependencies are missing
Also, it is probably worth pointing out that the flite.h header file in recent versions is by default located in a sub folder named "flite", so it might be better to use include <flite/flite.h> or instead adjust CXXFLAGS accordingly (on opensuse, /usr/local/include is used for the flite headers, instead of /usr/include/flite)