NanoVG link-phase warnings when using g++ "-O3 -flto" optimization flags.

[NielsMayer]

I recompiled the latest QNanoPainter after adding the following optimization tweaks to libqnanopainter/include.pri

## NPM: Turn optimization up to 11 for Release build.
## NPM: Use optimized debugging "-Og enables optimizations that do not interfere with debugging. It should be the optimization level of choice for the standard edit-compile-debug cycle, offering a reasonable level of optimization while maintaining fast compilation and a good debugging experience."
## https://gcc.gnu.org/onlinedocs/gcc-4.9.2/gcc/Optimize-Options.html
QMAKE_CFLAGS_OPTIMIZE_SIZE =  ##note that /opt/Qt5.12.0/5.12.0/android_armv7/mkspecs/common/gcc-base.conf sets this to "-Os" and uses for Android Arm builds (only) automatically. This unsets it and gives full optimized android arm builds.
QMAKE_CFLAGS_RELEASE   = -flto -ffast-math -O3
QMAKE_CFLAGS_DEBUG     = -g -Og
QMAKE_CXXFLAGS_RELEASE = -flto -ffast-math -O3
QMAKE_CXXFLAGS_DEBUG   = -g -Og
QMAKE_LFLAGS_RELEASE   = -flto -O3
QMAKE_LFLAGS_DEBUG     = -g -Og

In linking, the following strange warnings are produced related to NanoVG:

g++ -flto -O3 -Wl,-rpath,/opt/Qt5.12.0/5.12.0/gcc_64/lib -o qnanopainter_vs_qpainter_demo main.o demoqpitem.o demoqnanoitem.o demoqnanoitempainter.o qnanopainter.o qnanocolor.o qnanolineargradient.o qnanoimagepattern.o qnanoimage.o qnanofont.o qnanoradialgradient.o qnanoboxgradient.o qnanowindow.o qnanodebug.o qnanoquickitem.o qnanoquickitempainter.o qnanobackendgl2.o qnanobackendgl3.o nanovg.o qrc_qml_qmlcache.o qrc_libqnanopainterdata.o main_qml.o qml_Button_qml.o qml_FpsItem_qml.o qml_TabView_qml.o qml_SliderSelector_qml.o qml_Switch_qml.o qml_SettingsView_qml.o qml_shapeitem_RulerComponent_qml.o qml_shapeitem_FlowerComponent_qml.o qml_shapeitem_LinesComponent_qml.o qml_shapeitem_DemoShapeItem_qml.o qml_shapeitem_BarsComponent_qml.o qml_shapeitem_IconsComponent_qml.o qml_shapeitem_CirclesComponent_qml.o qmlcache_loader.o moc_demoqpitem.o moc_demoqnanoitem.o moc_qnanowindow.o moc_qnanoquickitem.o   -L/opt/Qt5.12.0/5.12.0/gcc_64/lib -lQt5Quick -lQt5Gui -lQt5Qml -lQt5Network -lQt5Core -lGL -lpthread   
../../../qnanopainter/libqnanopainter/nanovg/nanovg_gl_wrapped.h:231:8: warning: type ‘struct GLNVGcontext’ violates the C++ One Definition Rule [-Wodr]
 struct GLNVGcontext {
        ^
make[1]: Leaving directory '/usr/local/src/build-qnanopainter-Qt5_12_0_Desktop_GCC_C_x86_64bit_in_usr_bin-Release/examples/helloitem'
../../../qnanopainter/libqnanopainter/nanovg/nanovg_gl_wrapped.h:231:8: note: a different type is defined in another translation unit
 struct GLNVGcontext {
        ^
../../../qnanopainter/libqnanopainter/nanovg/nanovg_gl_wrapped.h:245:6: note: the first difference of corresponding definitions is field ‘fragSize’
  int fragSize;
      ^
../../../qnanopainter/libqnanopainter/nanovg/nanovg_gl_wrapped.h:240:9: note: a field with different name is defined in another translation unit
  GLuint vertArr;
         ^
../../../qnanopainter/libqnanopainter/nanovg/nanovg_gl_wrapped.h:231:8: warning: type ‘struct GLNVGcontext’ violates the C++ One Definition Rule [-Wodr]
 struct GLNVGcontext {
        ^
../../../qnanopainter/libqnanopainter/nanovg/nanovg_gl_wrapped.h:231:8: note: a different type is defined in another translation unit
 struct GLNVGcontext {
        ^
../../../qnanopainter/libqnanopainter/nanovg/nanovg_gl_wrapped.h:245:6: note: the first difference of corresponding definitions is field ‘fragSize’
  int fragSize;
      ^
../../../qnanopainter/libqnanopainter/nanovg/nanovg_gl_wrapped.h:240:9: note: a field with different name is defined in another translation unit
  GLuint vertArr;
         ^
make[1]: Leaving directory '/usr/local/src/build-qnanopainter-Qt5_12_0_Desktop_GCC_C_x86_64bit_in_usr_bin-Release/examples/hellowindow'
../../../qnanopainter/libqnanopainter/nanovg/nanovg_gl_wrapped.h:231:8: warning: type ‘struct GLNVGcontext’ violates the C++ One Definition Rule [-Wodr]
 struct GLNVGcontext {
        ^
../../../qnanopainter/libqnanopainter/nanovg/nanovg_gl_wrapped.h:231:8: note: a different type is defined in another translation unit
 struct GLNVGcontext {
        ^
../../../qnanopainter/libqnanopainter/nanovg/nanovg_gl_wrapped.h:245:6: note: the first difference of corresponding definitions is field ‘fragSize’
  int fragSize;
      ^
../../../qnanopainter/libqnanopainter/nanovg/nanovg_gl_wrapped.h:240:9: note: a field with different name is defined in another translation unit
  GLuint vertArr;
         ^
make[1]: Leaving directory '/usr/local/src/build-qnanopainter-Qt5_12_0_Desktop_GCC_C_x86_64bit_in_usr_bin-Release/examples/gallery'
../../../qnanopainter/libqnanopainter/nanovg/nanovg_gl_wrapped.h:231:8: warning: type ‘struct GLNVGcontext’ violates the C++ One Definition Rule [-Wodr]
 struct GLNVGcontext {
        ^
../../../qnanopainter/libqnanopainter/nanovg/nanovg_gl_wrapped.h:231:8: note: a different type is defined in another translation unit
 struct GLNVGcontext {
        ^
../../../qnanopainter/libqnanopainter/nanovg/nanovg_gl_wrapped.h:245:6: note: the first difference of corresponding definitions is field ‘fragSize’
  int fragSize;
      ^
../../../qnanopainter/libqnanopainter/nanovg/nanovg_gl_wrapped.h:240:9: note: a field with different name is defined in another translation unit
  GLuint vertArr;
         ^
make[1]: Leaving directory '/usr/local/src/build-qnanopainter-Qt5_12_0_Desktop_GCC_C_x86_64bit_in_usr_bin-Release/examples/hellowidget'
../../../qnanopainter/libqnanopainter/nanovg/nanovg_gl_wrapped.h:231:8: warning: type ‘struct GLNVGcontext’ violates the C++ One Definition Rule [-Wodr]
 struct GLNVGcontext {
        ^
../../../qnanopainter/libqnanopainter/nanovg/nanovg_gl_wrapped.h:231:8: note: a different type is defined in another translation unit
 struct GLNVGcontext {
        ^
../../../qnanopainter/libqnanopainter/nanovg/nanovg_gl_wrapped.h:245:6: note: the first difference of corresponding definitions is field ‘fragSize’
  int fragSize;
      ^
../../../qnanopainter/libqnanopainter/nanovg/nanovg_gl_wrapped.h:240:9: note: a field with different name is defined in another translation unit
  GLuint vertArr;
         ^

I am using Kubuntu 18.04LTS installed g++: "g++ (Ubuntu 7.3.0-27ubuntu1~18.04) 7.3.0"