src/Tools/Setup/etc/build.props

proper support for "isabelle update -D DIR": avoid accidental exclusion of select_dirs (amending e5dafe9e120f);

module = $ISABELLE_SETUP_JAR
no_build = true
sources = \
  src/Build.java \
  src/Environment.java \
  src/Exn.java \
  src/Library.java \
  src/Setup.java