Hello :)!

Description of problem:
With Fedora's 34 build of mingw-gtkmm30, when trying to build NoteKit, we have encountered some linking issues which do not happen with Fedora 33.

We get complaints from the linker about it being unable to find references of Gtk::TextIter.

Version-Release number of selected component (if applicable):
mingw-gtkmm30-3.24.4-1.fc34 (maybe 3.24.3)

How reproducible:
Always

Steps to Reproduce:
1. Building NoteKit with mingw & Fedora 34
2. Meditating in front of the linker issues

Actual results:
```
/usr/bin/x86_64-w64-mingw32-g++  -o notekit.exe notekit.exe.p/drawing.cpp.obj notekit.exe.p/imagewidgets.cpp.obj notekit.exe.p/main.cpp.obj notekit.exe.p/mainwindow.cpp.obj notekit.exe.p/navigation.cpp.obj notekit.exe.p/notebook.cpp.obj -Wl,--allow-shlib-undefined -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions --param=ssp-buffer-size=4 -mwindows -fstack-protector -Wl,--start-group -lssp -mwindows -Wl,--subsystem,windows /usr/x86_64-w64-mingw32/sys-root/mingw/lib/libgtkmm-3.0.dll.a /usr/x86_64-w64-mingw32/sys-root/mingw/lib/libatkmm-1.6.dll.a /usr/x86_64-w64-mingw32/sys-root/mingw/lib/libgdkmm-3.0.dll.a /usr/x86_64-w64-mingw32/sys-root/mingw/lib/libgiomm-2.4.dll.a /usr/x86_64-w64-mingw32/sys-root/mingw/lib/libgtk-3.dll.a /usr/x86_64-w64-mingw32/sys-root/mingw/lib/libgdk-3.dll.a /usr/x86_64-w64-mingw32/sys-root/mingw/lib/libgdi32.a /usr/x86_64-w64-mingw32/sys-root/mingw/lib/libimm32.a /usr/x86_64-w64-mingw32/sys-root/mingw/lib/libshell32.a /usr/x86_64-w64-mingw32/sys-root/mingw/lib/libole32.a -Wl,-luuid /usr/x86_64-w64-mingw32/sys-root/mingw/lib/libwinmm.a /usr/x86_64-w64-mingw32/sys-root/mingw/lib/libdwmapi.a /usr/x86_64-w64-mingw32/sys-root/mingw/lib/libsetupapi.a /usr/x86_64-w64-mingw32/sys-root/mingw/lib/libcfgmgr32.a /usr/x86_64-w64-mingw32/sys-root/mingw/lib/libpangowin32-1.0.dll.a /usr/x86_64-w64-mingw32/sys-root/mingw/lib/libatk-1.0.dll.a /usr/x86_64-w64-mingw32/sys-root/mingw/lib/libcairo-gobject.dll.a /usr/x86_64-w64-mingw32/sys-root/mingw/lib/libgio-2.0.dll.a /usr/x86_64-w64-mingw32/sys-root/mingw/lib/libpangomm-1.4.dll.a /usr/x86_64-w64-mingw32/sys-root/mingw/lib/libglibmm-2.4.dll.a /usr/x86_64-w64-mingw32/sys-root/mingw/lib/libcairomm-1.0.dll.a /usr/x86_64-w64-mingw32/sys-root/mingw/lib/libsigc-2.0.dll.a /usr/x86_64-w64-mingw32/sys-root/mingw/lib/libpangocairo-1.0.dll.a /usr/x86_64-w64-mingw32/sys-root/mingw/lib/libpango-1.0.dll.a /usr/x86_64-w64-mingw32/sys-root/mingw/lib/libharfbuzz.dll.a /usr/x86_64-w64-mingw32/sys-root/mingw/lib/libcairo.dll.a /usr/x86_64-w64-mingw32/sys-root/mingw/lib/libgdk_pixbuf-2.0.dll.a /usr/x86_64-w64-mingw32/sys-root/mingw/lib/libgobject-2.0.dll.a /usr/x86_64-w64-mingw32/sys-root/mingw/lib/libglib-2.0.dll.a /usr/x86_64-w64-mingw32/sys-root/mingw/lib/libintl.dll.a /usr/x86_64-w64-mingw32/sys-root/mingw/lib/libgtksourceviewmm-3.0.dll.a /usr/x86_64-w64-mingw32/sys-root/mingw/lib/libgtksourceview-3.0.dll.a /usr/x86_64-w64-mingw32/sys-root/mingw/lib/libjsoncpp.dll.a /usr/x86_64-w64-mingw32/sys-root/mingw/lib/libz.dll.a /usr/x86_64-w64-mingw32/sys-root/mingw/lib/libfontconfig.dll.a /usr/x86_64-w64-mingw32/sys-root/mingw/lib/libfreetype.dll.a /usr/x86_64-w64-mingw32/sys-root/mingw/lib/libclatexmath.dll.a -Wl,--subsystem,console -lkernel32 -luser32 -lgdi32 -lwinspool -lshell32 -lole32 -loleaut32 -luuid -lcomdlg32 -ladvapi32 -Wl,--end-group
/usr/lib/gcc/x86_64-w64-mingw32/10.3.1/../../../../x86_64-w64-mingw32/bin/ld: notekit.exe.p/notebook.cpp.obj: in function `CNotebook::on_insert(Gtk::TextIter const&, Glib::ustring const&, int)':
/root/notekit/x86_64-w64-mingw32/../notebook.cpp:291: undefined reference to `__imp__ZN3GtkgeERKNS_8TextIterES2_'
/usr/lib/gcc/x86_64-w64-mingw32/10.3.1/../../../../x86_64-w64-mingw32/bin/ld: /root/notekit/x86_64-w64-mingw32/../notebook.cpp:284: undefined reference to `__imp__ZN3GtkgeERKNS_8TextIterES2_'
/usr/lib/gcc/x86_64-w64-mingw32/10.3.1/../../../../x86_64-w64-mingw32/bin/ld: /root/notekit/x86_64-w64-mingw32/../notebook.cpp:277: undefined reference to `__imp__ZN3GtkgeERKNS_8TextIterES2_'
/usr/lib/gcc/x86_64-w64-mingw32/10.3.1/../../../../x86_64-w64-mingw32/bin/ld: /root/notekit/x86_64-w64-mingw32/../notebook.cpp:298: undefined reference to `__imp__ZN3GtkeqERKNS_8TextIterES2_'
/usr/lib/gcc/x86_64-w64-mingw32/10.3.1/../../../../x86_64-w64-mingw32/bin/ld: notekit.exe.p/notebook.cpp.obj: in function `CNotebook::on_redraw_overlay(Cairo::RefPtr<Cairo::Context> const&)':
/root/notekit/x86_64-w64-mingw32/../notebook.cpp:344: undefined reference to `__imp__ZN3GtkltERKNS_8TextIterES2_'
/usr/lib/gcc/x86_64-w64-mingw32/10.3.1/../../../../x86_64-w64-mingw32/bin/ld: notekit.exe.p/notebook.cpp.obj: in function `CNotebook::CleanUpSpan(Gtk::TextIter&, Gtk::TextIter&)':
/root/notekit/x86_64-w64-mingw32/../notebook.cpp:651: undefined reference to `__imp__ZN3GtkneERKNS_8TextIterES2_'
/usr/lib/gcc/x86_64-w64-mingw32/10.3.1/../../../../x86_64-w64-mingw32/bin/ld: /root/notekit/x86_64-w64-mingw32/../notebook.cpp:672: undefined reference to `__imp__ZN3GtkltERKNS_8TextIterES2_'
/usr/lib/gcc/x86_64-w64-mingw32/10.3.1/../../../../x86_64-w64-mingw32/bin/ld: /root/notekit/x86_64-w64-mingw32/../notebook.cpp:645: undefined reference to `__imp__ZN3GtkgtERKNS_8TextIterES2_'
/usr/lib/gcc/x86_64-w64-mingw32/10.3.1/../../../../x86_64-w64-mingw32/bin/ld: /root/notekit/x86_64-w64-mingw32/../notebook.cpp:686: undefined reference to `__imp__ZN3GtkneERKNS_8TextIterES2_'
/usr/lib/gcc/x86_64-w64-mingw32/10.3.1/../../../../x86_64-w64-mingw32/bin/ld: /root/notekit/x86_64-w64-mingw32/../notebook.cpp:681: undefined reference to `__imp__ZN3GtkgtERKNS_8TextIterES2_'
/usr/lib/gcc/x86_64-w64-mingw32/10.3.1/../../../../x86_64-w64-mingw32/bin/ld: notekit.exe.p/notebook.cpp.obj: in function `CNotebook::on_serialize(Glib::RefPtr<Gtk::TextBuffer> const&, Gtk::TextIter const&, Gtk::TextIter const&, unsigned long long&, bool)':
/root/notekit/x86_64-w64-mingw32/../notebook.cpp:1223: undefined reference to `__imp__ZN3GtkneERKNS_8TextIterES2_'
/usr/lib/gcc/x86_64-w64-mingw32/10.3.1/../../../../x86_64-w64-mingw32/bin/ld: notekit.exe.p/notebook.cpp.obj: in function `CNotebook::CommitStroke()':
/root/notekit/x86_64-w64-mingw32/../notebook.cpp:1122: undefined reference to `__imp__ZN3GtkeqERKNS_8TextIterES2_'
/usr/lib/gcc/x86_64-w64-mingw32/10.3.1/../../../../x86_64-w64-mingw32/bin/ld: /root/notekit/x86_64-w64-mingw32/../notebook.cpp:1155: undefined reference to `__imp__ZN3GtkneERKNS_8TextIterES2_'
/usr/lib/gcc/x86_64-w64-mingw32/10.3.1/../../../../x86_64-w64-mingw32/bin/ld: notekit.exe.p/notebook.cpp.obj: in function `CNotebook::DebugTags(Gtk::TextIter&, Gtk::TextIter&)':
/root/notekit/x86_64-w64-mingw32/../notebook.cpp:444: undefined reference to `__imp__ZN3GtkltERKNS_8TextIterES2_'
/usr/lib/gcc/x86_64-w64-mingw32/10.3.1/../../../../x86_64-w64-mingw32/bin/ld: notekit.exe.p/notebook.cpp.obj: in function `CNotebook::on_leave_region(Gtk::TextIter&, Gtk::TextIter&)':
/root/notekit/x86_64-w64-mingw32/../notebook.cpp:739: undefined reference to `__imp__ZN3GtkltERKNS_8TextIterES2_'
/usr/lib/gcc/x86_64-w64-mingw32/10.3.1/../../../../x86_64-w64-mingw32/bin/ld: notekit.exe.p/notebook.cpp.obj: in function `CNotebook::on_highlight_updated(Gtk::TextIter&, Gtk::TextIter&)':
/root/notekit/x86_64-w64-mingw32/../notebook.cpp:382: undefined reference to `__imp__ZN3GtkltERKNS_8TextIterES2_'
/usr/lib/gcc/x86_64-w64-mingw32/10.3.1/../../../../x86_64-w64-mingw32/bin/ld: notekit.exe.p/notebook.cpp.obj:/root/notekit/x86_64-w64-mingw32/../notebook.cpp:841: undefined reference to `__imp__ZN3GtkeqERKNS_8TextIterES2_'
/usr/lib/gcc/x86_64-w64-mingw32/10.3.1/../../../../x86_64-w64-mingw32/bin/ld: notekit.exe.p/notebook.cpp.obj: in function `operator()':
/root/notekit/x86_64-w64-mingw32/../notebook.cpp:816: undefined reference to `__imp__ZN3GtkeqERKNS_8TextIterES2_'
/usr/lib/gcc/x86_64-w64-mingw32/10.3.1/../../../../x86_64-w64-mingw32/bin/ld: notekit.exe.p/notebook.cpp.obj: in function `CNotebook::SelectBox(float, float, float, float)':
/root/notekit/x86_64-w64-mingw32/../notebook.cpp:1080: undefined reference to `__imp__ZN3GtkeqERKNS_8TextIterES2_'
/usr/lib/gcc/x86_64-w64-mingw32/10.3.1/../../../../x86_64-w64-mingw32/bin/ld: /root/notekit/x86_64-w64-mingw32/../notebook.cpp:1082: undefined reference to `__imp__ZN3GtkneERKNS_8TextIterES2_'
collect2: error: ld returned 1 exit status
ninja: build stopped: subcommand failed.
```

Expected results:
Successful build

Additional info:
Here is an example of a failing CI:
https://github.com/sp1ritCS/notekit/runs/2504999899

Using this recipe:
https://github.com/sp1ritCS/notekit/blob/e0912a7b56e2b09ca041f448c2223fe403454672/.github/workflows/windows.yml

Additionally, there seems to be a related open issue on GitHub:
https://github.com/msys2/MINGW-packages/issues/8008

Also, @sp1ritCS suspects this PR[1] might be the cause:
https://gitlab.gnome.org/GNOME/gtkmm/-/merge_requests/25/diffs#69b7ccb873aba60a8764970f0423303e17729a51

It could be nice to have this fixed, in Fedora at least :)!

Also, thank you for maintaining this mingw package :)!