Use CMAKE_CROSSCOMPILING_EMULATOR in FindPythonInterp.cmake

This allows to use FindPythonInterp in a cross-compiling context where we want to use the target python without relying on binfmt_misc, thus lifting for example the requirement of wine on the host of a docker build.

I dont know if we have to consider the case where we want to cross-compile, but detect python of the host (use it as a code generation tool for example).