Fix lime.ndll build on MinGW

[tobil4sk]

Fixes some issues to allow compiling lime.ndll with MinGW.

I'm not too sure what the best way to deal with the System.cpp situation would be.

[tobil4sk]

I separated out some of the commits into #1661, because with those commits it's already possible to cross compile projects with mingw with a precompiled lime.ndll.

[DigiEggz]

I'm interested in testing this build! Could you offer any links to the new precompiled minGW version of lime.ndll? If not, I can look into building from source, but it might be a while.

[tobil4sk]

I'm interested in testing this build! Could you offer any links to the new precompiled minGW version of lime.ndll?

Hi sorry, I haven't uploaded the precompiled lime.ndll anywhere. Building from source isn't too complicated as long as you have mingw set up, when I have a look at this again I can try to provide some proper instructions for how to do this. I should have provided instructions originally in the PR, sorry. Once I have a look again I could probably upload a copy of the ndll here as well.

Just a heads up, I managed to get things compiling but the build wasn't really working. When I tried to run a project with the mingw ndll there was no window showing up unfortunately. This will require more investigating to figure out what exactly is wrong. In the meantime I have just been building my actual project code with mingw (with #1661 and the git version of hxcpp) but using the regular Windows lime.ndlls instead of compiling my own mingw copy.

[DigiEggz]

I'm interested in testing this build! Could you offer any links to the new precompiled minGW version of lime.ndll?

Hi sorry, I haven't uploaded the precompiled lime.ndll anywhere. Building from source isn't too complicated as long as you have mingw set up, when I have a look at this again I can try to provide some proper instructions for how to do this. I should have provided instructions originally in the PR, sorry. Once I have a look again I could probably upload a copy of the ndll here as well.

Just a heads up, I managed to get things compiling but the build wasn't really working. When I tried to run a project with the mingw ndll there was no window showing up unfortunately. This will require more investigating to figure out what exactly is wrong. In the meantime I have just been building my actual project code with mingw (with #1661 and hxcpp patches HaxeFoundation/hxcpp#1044 HaxeFoundation/hxcpp#1045 HaxeFoundation/hxcpp#1046) but using the regular Windows lime.ndlls instead of compiling my own mingw copy.

I'll give that a try! Thanks again for all of the work you've put into this build.

[DigiEggz]

When trying compiling my app (with this library), I get an error:
Error: /Users/E/Documents/Haxe/hxdiscord_rpc/git/project/discord-rpc/src/connection_win.cpp:8:10: fatal error: 'windows.h' file not found

Do you know what I may have to do in order to get the windows.h header file to be included? I'm not sure if I haven't linked minGW or if it's otherwise not set up correctly.

Edit: I used this guide to manually set some of my paths. I cannot compile to 32-bit (he -32 flag doesn't change anything) and trying to set the MINGW_ROOT path results in a double-concatenated string for some reason, but it otherwise works.