Win: Enable testing cross-compiled builds

Win: Enable testing cross-compiled builds

When cross-compiling, CMakeLists.txt now generates the CTest script
using relative paths, so that CTest can more easily be executed on a
different machine from the build machine.  Furthermore, Windows builds
are now tested using md5cmp, just like on Linux, rather than a CMake
script.  This prevents issues with differing CMake locations between
the build and test machines.

This also removes some trailing spaces from the md5cmp code and improves
the readability of the test code in CMakeLists.txt.