Jem Aswad Senior Music EditorSinger-songwriter Rhiannon Giddens, accompanied virtually by virtuoso cellist Yo-Yo Ma, has released a new song called “Build a House” in honor of Juneteenth.“This song, ‘Build a House,’ came knocking a week ago and I had to let it in,” Giddens wrote in a Twitter message accompanying the nearly five-minute-long song, which features split video of her performing it with Ma.