[Cross Platform] Add cross platform support to compile script

[kudaba]

I use this to build for all platforms from my windows machine.

I used to use /p:PublishSingleFile=true to reduce the number of dependent dlls generated, however recent changes means that you can't reference module filenames when in that mode which breaks a lot of sharpmake code. It would be great to support that feature eventually so the linux/max executables are only a few files instead of ~200.