on cygwin, configure forced TMPDIR to /tmp, regardless whether it is set
or not. And while it respects an existing value of TMP, TMP is only used
in a few places. Changes the ones that explicitly check for TMP to
prefer TMPDIR, and don't duplicate configure's check in other scripts.

Change-Id: Ia8ac3f8d92e5f971c5237b85f66f7c0a58932930
Reviewed-on: https://gerrit.libreoffice.org/3701Reviewed-by: David Tardon <dtardon@redhat.com>
Tested-by: David Tardon <dtardon@redhat.com>