This option should be used if the package has been ported to build clean dlls on win32 platforms. Usually this means that any library data items are exported with declspec(dllexport) and imported with declspec(dllimport). If this option is not used, libtool will assume that the package libraries are not dll clean and will build only static libraries on win32 hosts.
Provision must be made to pass -no-undefined to libtool in link mode from the package Makefile. Naturally, if you pass -no-undefined, you must ensure that all the library symbols really are defined at link time!
Due to Windows platform limitations, this option is required when building shared libraries. Without this option, only static libraries can be built.
https://www.gnu.org/software/libtool/manual/html_node/LT_005fINIT.html