Log Message:
google-benchmark: update to 1.5.6.

features

    helper methods to create integer lists (#1179)
    default of --benchmark_filter is now rather than "." (#1207)

fixes

    type warning (#1193)
    returning a reference when callers want pointers (65dc63b)

cleanup

    remove dead code from PredictNumItersNeeded (#1206)
    fix clang-tidy warnings (#1195) and typos (#1194)
    prefix macros (#1186) and flags (#1187, #1185) to avoid name clashes
    downgrade warnings for googletest (twice) (#1203, 560b0834, ee726a7)