Create Xcode project for existing cross-platform file structure

Create Xcode project for existing cross-platform file structure

I am creating a C++ static library which is meant to be compilable on
Windows, OSX/iOS, or Linux. At the moment, the existing directory
structure is:
LibraryRoot
.git - git repository
Core - core OS independent source code
OSX - OSX specific code, including Xcode project files
Windows - Windows specific code, including developer studio project
files
Linux - Linux stuff
I dont understand how to create the project using this file structure
within Xcode. It seems that Xcode wants to create a directory with the
project name and put a new repository and project files inside, which is
not what I want here. Also I'm not sure how to make Xcode recognize the
git repository which is above the directory which is intended to host the
Xcode project files. I don't need to create any special makefile or rules
outside of the Xcode project file.
Is doing it this way possible with Xcode?