IF you have the source code, Yes winmain can be helpful.

if your code has Microsoft Macros and APIs all over the place, Winmain will port it to a target platform  which in your case is Linux

if the code is (considering it's written in C family) Ansi compliant, you can port the code into a posix based environment and build a shared object. This is in a case that you are not keeping the source platform though, otherwise interfacing to the original platform was the best way.

I have used Java ActiveX bridge to convert POJO to .tld (DLL control) but I imagined it could do the reverse as well, it's a bridge after all. If you say it doesn't do it, no argue with that. wasn't too sure anyway. but I thought I've seen somewhere in it's notes. worth checking