Hydropower uses massive amounts of cement, and the cement industry is responsible for about 5% of all carbon emissions. Similarly, if you're counting the environmental impact of manufacturing the more energy-efficient computer, you must also count the environmental impact of the solar panels or wind turbines that do not have to be manufactured because of the increased energy efficiency.
Surely the one-time emissions in cement required to build a dam that lasts for decades amortizes down to nothing compared with the ongoing outputs associated with coal or gas fired electricity production? (not to mention the upfront emissions associated with constructing those facilities as well...)
Most of those global cement emissions are surely in building sidewalks, highways, bridges, and skyscrapers? Seems weird to blame an otherwise pretty green electricity source for this carbon.
