buildconf.sh: Create missing conftools/install-sh

Otherwise configure will fail with:
configure: error: cannot find install-sh, install.sh, or shtool in conftools "."/conftools
1 file changed
tree: 3713afd4b0d70a792a7a5b0ec6948945c4b943b1
  1. .gitignore
  2. expat/
  3. htdocs/
  4. testdata/