The filesystem root directory includes a text file named "build_info.txt". Here's an example:
2015_12_22 Linux SHA:e739692bda7615008919e949245e079df35c7061 Linux branch:2015_R1 Linux repository:github.com/.../linux.git HDL SHA:2130b15035f40364de05ad23e5995de417f3c11c HDL branch:hdl_2015_r1 HDL repository:github.com/.../hdl.git