Moves the library compilation into Platform specific directory

[AndreaCatania]

This is the first PR to enable CrossCompilation support with this plugin.

As suggested here, the compilation is now executed in platform-specific folders.

Before: MyUEProject\Intermediate\CMakeTarget\TheLibrary Now: MyUEProject\Intermediate\CMakeTarget\TheLibrary\Win64 and MyUEProject\Intermediate\CMakeTarget\TheLibrary\Linux