ninjabackend/vs: handle builddir on different drive from cwd
ninjabackend/vs: handle builddir on different drive from cwd

When setup creates a Visual Studio environment, a message is logged
which contains a path to the build directory. Typically, this path is
converted to a relative path prior to printing. If the path cannot be
converted to a relative path (e.g., because buildpath is on a different
drive from the cwd), print out the full path instead of failing with an
unhandled exception.

mesonbuild/meson,pexip/meson,pexip/meson,mesonbuild/meson,mesonbuild/meson,pexip/meson,pexip/meson,mesonbuild/meson,pexip/meson,pexip/meson,pexip/meson,mesonbuild/meson,mesonbuild/meson,mesonbuild/meson,mesonbuild/meson,pexip/meson,mesonbuild/meson,mesonbuild/meson,pexip/meson,pexip/meson