BUG: DatetimeIndex(dt64_unsupported) raises

[jbrockmendel]

vals = [np.datetime64(1, "D")]

>>> pd.DatetimeIndex(vals, tz="US/Pacific")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "pandas/core/indexes/datetimes.py", line 356, in __new__
    dtarr = DatetimeArray._from_sequence_not_strict(
  File "pandas/core/arrays/datetimes.py", line 329, in _from_sequence_not_strict
    subarr, tz, inferred_freq = _sequence_to_dt64ns(
  File "pandas/core/arrays/datetimes.py", line 2126, in _sequence_to_dt64ns
    data = tzconversion.tz_localize_to_utc(
  File "pandas/_libs/tslibs/tzconversion.pyx", line 239, in pandas._libs.tslibs.tzconversion.tz_localize_to_utc
    Localizer info = Localizer(tz, creso=creso)
  File "pandas/_libs/tslibs/tzconversion.pyx", line 100, in pandas._libs.tslibs.tzconversion.Localizer.__cinit__
    raise NotImplementedError(creso)
NotImplementedError: 4