Don't package settings in bindist

Since !712 the `settings` file is produced by the build system instead
of autoconf. However, this introduced a subtle bug where we would fail
to rebuild the `settings` file with what we have learned from the
install-time `configure` invocation. Fix this by not packaging
`settings` in the bindist tarball. The build system will take care of
the rest.

Also fix a bug where the value of `UseLibdw` was not being persisted to
the install time `configure`.