fix creating dict with JIT disabled

[esc]

When using NUMBA_DISABLE_JIT=1 we still want dictobject.new_dict to
work, for example to measure coverage and such things.

[seibert]

Seems reasonable to me.

[seibert]

Following on Stuart's suggestion from #4920, the test could be made to more directly verify the DISABLE_JIT behavior with this test pattern:

numba/numba/tests/test_debug.py

Lines 184 to 188 in 92dbdb9

	def test_jit(self):
	with override_config('DISABLE_JIT', True):
	with forbid_codegen():
	cfunc = jit(nopython=True)(simple_nopython)
	self.assertPreciseEqual(cfunc(2), 3)

[esc]

So the dictobject.new_dict and Dict.empty 'constructors' work now. Dict() also works with the JIT disabled but returns a Dict instance rather than a dict instance. While this might look O.K. from a testing perspective, any attempt to mutate the Dict instance when DISABLE_JIT is active will most likely lead to an error, so the test for that is an expected failure for now.

[esc]

Fixed Dict too cc @seibert

[seibert]

looks good!