int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    MySystemTray st;

    QApplication::setQuitOnLastWindowClosed(false);

    return a.exec();

}

MySystemTray::MySystemTray(QWidget* pwgt):QLabel("<H1>GLab</H1>",pwgt)
    
{
     window= new MainWindow(this);
     window->show();
}

qt5-default
qtcreator
libqtcore5  

Reading package lists... Done
Building dependency tree       
Reading state information... Done
g++ is already the newest version (4:5.3.1-1ubuntu1).
g++ set to manually installed.
The following packages were automatically installed and are no longer required:
  libdrm-dev libdrm-exynos1 libdrm-omap1 libdrm-tegra0 libegl1-mesa-dev libgles2-mesa-dev libllvm3.8
  libmirclient-dev libmircommon-dev libmircommon5 libmircookie-dev libmircookie2 libmircore-dev
  libprotobuf-dev libprotobuf9v5 libpthread-stubs0-dev libwayland-bin libwayland-dev libx11-dev
  libx11-xcb-dev libxau-dev libxcb-dri2-0-dev libxcb-dri3-dev libxcb-glx0-dev libxcb-present-dev
  libxcb-randr0-dev libxcb-render0-dev libxcb-shape0-dev libxcb-sync-dev libxcb-xfixes0-dev libxcb1-dev
  libxdamage-dev libxdmcp-dev libxext-dev libxfixes-dev libxkbcommon-dev libxshmfence-dev libxxf86vm-dev
  qtbase5-dev x11proto-core-dev x11proto-damage-dev x11proto-dri2-dev x11proto-fixes-dev x11proto-gl-dev
  x11proto-input-dev x11proto-kb-dev x11proto-xext-dev x11proto-xf86vidmode-dev xorg-sgml-doctools
  xtrans-dev
Use 'sudo apt autoremove' to remove them.
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.

Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/lib/gcc/arm-linux-gnueabihf/5/lto-wrapper
Target: arm-linux-gnueabihf
Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro 5.4.0-6ubuntu1~16.04.5' --with-bugurl=file:///usr/share/doc/gcc-5/README.Bugs --enable-languages=c,ada,c++,java,go,d,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-5 --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new --enable-gnu-unique-object --disable-libitm --disable-libquadmath --enable-plugin --with-system-zlib --disable-browser-plugin --enable-java-awt=gtk --enable-gtk-cairo --with-java-home=/usr/lib/jvm/java-1.5.0-gcj-5-armhf/jre --enable-java-home --with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-5-armhf --with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-5-armhf --with-arch-directory=arm --with-ecj-jar=/usr/share/java/eclipse-ecj.jar --enable-objc-gc --enable-multiarch --enable-multilib --disable-sjlj-exceptions --with-arch=armv7-a --with-fpu=vfpv3-d16 --with-float=hard --with-mode=thumb --disable-werror --enable-multilib --enable-checking=release --build=arm-linux-gnueabihf --host=arm-linux-gnueabihf --target=arm-linux-gnueabihf
Thread model: posix
gcc version 5.4.0 20160609 (Ubuntu/Linaro 5.4.0-6ubuntu1~16.04.5) 

qt5-qmake
qt5-default
qtcreator
libqtcore5 
qmake

sudo apt-get install libxcb1-dev libxcb-image0-dev libxcb-keysyms1-dev libxcb-icccm4-dev libxcb-render-util0-dev libxcb-util0-dev libxrender-dev libasound-dev libpulse-dev libxcb-sync0-dev libxcb-xfixes0-dev libxcb-randr0-dev libx11-xcb-dev libffi-dev

screen

git clone git://code.qt.io/qt/qt5.git qt5.5.1
cd qt5.5.1
git checkout 5.5
perl init-repository --module-subset=qtbase,qtserialport, qtimageformats,qtscript,qtdeclarative
git checkout v5.5.1
cd qtimageformats && git checkout v5.5.1 && cd ..
cd qtbase && git checkout v5.5.1 && cd ..
cd qtscript && git checkout v5.5.1 && cd ..
cd qtdeclarative && git checkout v5.5.1 && cd ..
cd qtserialport && git checkout v5.5.1 && cd ..

./configure -release -opensource -confirm-license -qt-zlib -qt-libpng -qt-libjpeg -qt-freetype -qt-harfbuzz -qt-pcre -qt-xcb -qt-xkbcommon-x11 -no-opengl -static -nomake examples -nomake tests -prefix /usr/local/qt5 |& tee output_configure

make -j4 |& tee output_make

sudo make -j4 install  |& tee output_make_install