add Feature checks for install_subdir creating an empty directory
add Feature checks for install_subdir creating an empty directory

Most importantly, tell people it's broken and to stop using it for
0.62.0

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