Add ARM support

For a project I was working on I thought it might be useful to utilize the packr launcher but there isn't an ARM build (or more specifically, a Raspberry Pi build).

I'm not sure the proper way of going about this, but I was able to get an ARM version built by doing the following:

1. Removing the platforms directive (platforms { "x32", "x64" }) located at the end of the premake4-linux.lua file
2. Edit the launcher.cpp file and change the jre assignment
   • From: std::string jre = execDir + std::string("/jre/lib/i386/server/libjvm.so");
   • To: std::string jre = execDir + std::string("/jre/lib/arm/client/libjvm.so");

With these changes I was able to compile it natively on the Raspberry Pi. I imagine this isn't the proper way to do this as I'm not using any defines, etc, but it worked so I figure it might be helpful and it would be much appreciated to see ARM support officially added to Packr.

Thank you!

Start with premake4-linux.lua and launcher.cpp, focusing on the platforms directive and the JRE library path described in the issue. Build the launcher natively on a Raspberry Pi and verify that the resulting ARM package launches successfully; done means ARM support is integrated rather than relying on manual local edits.