Comment # 3 on bug 1172059 from Ralf Habacker

(In reply to Ralf Habacker from comment #2)
> [ 1239s]     Installed (but unpackaged) file(s) found:
> [ 1239s]   
> /usr/lib/debug/.dwz/mingw32-libqt5-qtbase-5.12.12-lp153.3.9.x86_64

This indicates that there is no %package tag for the debug package present.

In /usr/lib/rpm/macros there is the following fragment

%debug_package \
%ifnarch noarch\
%global __debug_package 1\
%_debuginfo_template\
%{?_debugsource_packages:%_debugsource_template}\
%endif\
%{nil}

which excludes adding native debug packages when using a noarch architecture,
which is the default for generating mingw packages

The mentioned file belongs to

$ rpm -q -f /usr/lib/rpm/macros    
rpm-4.14.1-29.46.x86_64