Fix several issues on windows

[falkTX]

• posix named semaphores are not implemented in mingw https://github.com/mirror/mingw-w64/blob/master/mingw-w64-libraries/winpthreads/src/sem.c#L312
• GetModuleFileName used NULL, which would get the standalone/host path, not the plugin path. we need to get the handle from the DllMain function
• Also GetModuleFileName was used the ANSI variant, which breaks for any special characters, we should switch to use wide-char API variants
• getenv on windows does not work as we expect, and also has same ANSI variant issues, prefer to use GetEnvironmentVariableW
• adjust env var stuff to work for mod-app on windows.

with this the plugin loads without crashes and seems to work as intended even in mod-app. but I didnt test much

[brummer10]

Thanks for the fixes!