Check for ARM architecture

contains QMAKE_HOST raspberry arm

Source

• https://stackoverflow.com/a/39792865/12780516
• https://stackoverflow.com/a/76532117/12780516

linux {
    # this only works if building *on* a raspi
    #contains(QMAKE_HOST.arch, arm.*):{
    # this also works if cross-building for a raspi
    contains(QMAKESPEC, .*linux-rasp-pi\d*-.*) {
        # code for raspis
    } else {
        # code for all other Linuxes
    }
}