The problem is that the building is basically a crude concave mirror, that problem will persist any time the Sun is in the right parts of the sky, the building

The problem is that the building is basically a crude concave mirror, that problem will persist any time the Sun is in the right parts of the sky, the building continues to be the same shape, and the building's surface continues to be dominated by windows made of glass (or any material which has a similar degree of reflectivity, especially at high angles). There are simply no good, truly long-term solutions to this problem that do not involve drastic changes to the building. The best solution would likely be to do something about the windows on the concave side of the building, putting some sort of external shade on them, changing the angle each window faces, or something to disrupt the normal magnification effect. The correct solution is tearing down the monstrosity and building something that wasn't designed by an idiot in its place but that's likely too expensive to entertain at the moment.