gitlab-ci: mingw build

• 64bit pango fails to build (-Werror...), I'll look into that
  I've filed https://bugzilla.gnome.org/show_bug.cgi?id=795012 and
  https://bugzilla.gnome.org/show_bug.cgi?id=795045
• gtk fails to link with the subproject pango -> help wanted, I have no idea edit: newer pango is in msys2 now

FAILED: gtk/libgtk-4-0.9300.0.dll 
cc @gtk/libgtk-4-0.9300.0.dll.rsp
C:/msys64/MINGW32/bin/../lib/gcc/i686-w64-mingw32/7.3.0/../../../../i686-w64-mingw32/bin/ld.exe: warning: subprojects/pango/pango/libpango-1.0.dll.a(d000212.o): local symbol `ext' has no section
C:/msys64/MINGW32/bin/../lib/gcc/i686-w64-mingw32/7.3.0/../../../../i686-w64-mingw32/bin/ld.exe: warning: subprojects/pango/pango/libpango-1.0.dll.a(d000212.o): local symbol `0`.idata' has no section
C:/msys64/MINGW32/bin/../lib/gcc/i686-w64-mingw32/7.3.0/../../../../i686-w64-mingw32/bin/ld.exe: warning: subprojects/pango/pango/libpango-1.0.dll.a(d000212.o): local symbol `' has no section
collect2.exe: error: ld returned 1 exit status