fix gendocs

Author: deads2k

hack/common.sh

@@ -475,7 +475,7 @@ os::build::gen-docs() {
   # We do this in a tmpdir in case the dest has other non-autogenned files
   # We don't want to include them in the list of gen'd files
   local tmpdir="${OS_ROOT}/_tmp/gen_doc"
-  mkdir "${tmpdir}"
+  mkdir -p "${tmpdir}"
   # generate the new files
   ${cmd} "${tmpdir}"
   # create the list of generated files