Turns out these were needed after all.
message("-- Using Qt5")
find_package(Qt5Widgets REQUIRED)
find_package(Qt5Gui REQUIRED)
- set(CMAKE_CXX_FLAGS ${CMAKE_CXX_FLAGS} ${Qt5Widgets_EXECUTABLE_COMPILE_FLAGS})
+ set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${Qt5Widgets_EXECUTABLE_COMPILE_FLAGS}")
set(QT_INCLUDE_DIRS ${Qt5Gui_INCLUDE_DIRS} ${Qt5Widgets_INCLUDE_DIRS})
set(QT_LIBRARIES Qt5::Gui Qt5::Widgets)
add_definitions(${Qt5Gui_DEFINITIONS} ${Qt5Widgets_DEFINITIONS})