Are you still having this problem? I have been able to build a Perl dev environment in MinGW64, current as of this time.
I have been able to build Perl Gtk2 / Gtk3 applications in that environment and the GUIs work. (Both Gtk2 and Gtk3 based). These applications are used in a production environment with several thousand desktop users. The application runs on OSX, Windows, and Linux, and can be packed into a binary for release as an "executable" for those operating systems. The details here are for the Windows version.
I do this by either installing the requisite system packages first with pacman, then as necessary rebuilding whatever system library packages that I may have modified, from source, using makepkg-mingw.
Then I build the requisite Perl modules using the CPAN shell, and the "look" command.
I use pkg-config to detect what library and header files are needed.
I then build (at minimum), the Perl Glib, Pango, Cairo, Gtk2, and Gtk3 modules using the perl Makefile.PL
command.
The LIBS and INC options need to be added to that command to create a Makefile that includes the correct header files, and links to the correct libraries. The EXTRALIBS and LDLOADLIBS sections of the Makefile needs be correct.
Also ExtUtils::MM_Win32.pm ExtUtils::Liblist::Kid.pm needed to be edited due to the different archname reported by the MinGW64 perl.
I am only giving a general answer, because I was thinking offing a YouTube video on this. If this is a desired topic I will.