Comment # 1 on bug 1225808 from Ralf Habacker

Adding debug sources is started by rpmbuild by a call to 

/usr/lib/rpm/mingw64-find-debuginfo.sh /home/abuild/rpmbuild/BUILD 1

which work for example with mingw64-zlib

extracting debug info from
/home/abuild/rpmbuild/BUILDROOT/mingw64-zlib-1.2.13-0.x86_64/usr/x86_64-w64-mingw32/sys-root/mingw/bin/libminizip-1.dll
extracting debug info from
/home/abuild/rpmbuild/BUILDROOT/mingw64-zlib-1.2.13-0.x86_64/usr/x86_64-w64-mingw32/sys-root/mingw/bin/libz.dll
creating debugsource file structure
copying /home/abuild/rpmbuild/BUILD/zlib-1.2.13/adler32.c to
/home/abuild/rpmbuild/BUILDROOT/mingw64-zlib-1.2.13-0.x86_64/usr/x86_64-w64-mingw32/sys-root/mingw/src/debug/zlib-1.2.13/adler32.c
... 

while with mingw64-openssl

...
extracting debug info from
/home/abuild/rpmbuild/BUILDROOT/mingw64-openssl-1.0.2h-0.x86_64/usr/x86_64-w64-mingw32/sys-root/mingw/bin/libssl-10.dll
...
creating debugsource file structure
<empty list>

no files are copied.