When building Python, the setup.py script will use values from sysconfig, even when cross compiling. When cross compiling, the interpreter that runs setup.py is configured for the build system, not the host system, so the wrong values are used. This patch should fix that.

It should be noted that the updated script assumes it is run from the build directory (like the Makefile) and that the script is at the top-level source directory. Also it uses a private method from sysconfig. This is unavoidable without modifying the sysconfig interface (or duplicating code).