Connect it to the rail, i.e. the LDO output.
Consider swapping your power and ground planes so they're L3 and L2 respectively. Most signals end up on the top layer, because that's where most parts are, and the ground plane typically has lower impedance than the power. With ground in L2 it makes it super easy to put ground right under an XO, oscillator, reference clock network, or elsewhere where you think it might be beneficial - in fact, this is what just happens unless you go out of your way. Parts on the bottom often end up being decoupling and pull resistors, that connect to the power plane. Or card/battery holders, connectors, that kind of thing - maybe the occasional part that just didn't fit on top. Then, in the future, if you use blind vias you'll save substantial board real estate with this stackup. You'll develop habits and practices based on your stackup, and it's nice to immediately realize a gain if you do decide to pony up for blind vias. (Not much use for buried vias with either of these 4L stackups.
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